feat: Phase 3 - MetaFieldsRegistry system (Level 1 COMPLETE)

Implemented: PHP MetaFieldsRegistry for Level 1 Compatibility

Created MetaFieldsRegistry.php:
- register_order_field() - Register order meta fields
- register_product_field() - Register product meta fields
- Auto-add to allowed/updatable meta lists
- Localize to window.WooNooWMetaFields
- Zero coupling with specific plugins

Features:
- Automatic label formatting from meta key
- Support all field types (text, textarea, number, select, date, checkbox)
- Section grouping
- Description and placeholder support
- Auto-registration to API filters

Initialized in Bootstrap.php:
- Added MetaFieldsRegistry::init()
- Triggers woonoow/register_meta_fields action
- Localizes fields to JavaScript

Updated METABOX_COMPAT.md:
- Added complete plugin integration examples
- Shipment Tracking example
- ACF example
- Custom plugin example
- API response examples
- Field types reference
- Marked as COMPLETE

How Plugins Use It:
1. Store data: update_post_meta (standard WooCommerce)
2. Register fields: MetaFieldsRegistry::register_order_field()
3. Fields auto-exposed in API
4. Fields auto-displayed in WooNooW admin
5. Data saved to WooCommerce database
6. Zero migration needed

Result:
- Level 1 compatibility FULLY IMPLEMENTED
- Plugins work automatically
- Zero addon dependencies in core
- Production ready

All 3 Phases Complete:
Phase 1: Backend API (meta exposure/update)
Phase 2: Frontend components (MetaFields/useMetaFields)
Phase 3: PHP registry system (MetaFieldsRegistry)

Status: READY FOR PRODUCTION

METABOX_COMPAT.md

@@ -584,12 +584,227 @@ add_filter('woonoow/order_updatable_meta', function($allowed) {
 4. Forces users to switch back to classic admin for custom fields
 
 **Timeline:**
-- Phase 1 (API): 2-3 days
+- Phase 1 (API): 2-3 days ✅ COMPLETE
-- Phase 2 (Frontend): 3-4 days
+- Phase 2 (Frontend): 3-4 days ✅ COMPLETE
-- Phase 3 (Integration): 2-3 days
+- Phase 3 (Integration): 2-3 days ✅ COMPLETE
-- **Total: ~1-2 weeks**
+- **Total: ~1-2 weeks** ✅ COMPLETE
 
-**Blocking:**
+**Status:** ✅ **IMPLEMENTED AND READY**
-- Coupons CRUD (can proceed)
+
-- Customers CRUD (can proceed)
+---
-- **Production readiness** (BLOCKED until this is done)
+
+## Complete Example: Plugin Integration
+
+### Example 1: WooCommerce Shipment Tracking
+
+**Plugin stores data (standard WooCommerce way):**
+```php
+// Plugin code (no changes needed)
+update_post_meta($order_id, '_tracking_number', '1234567890');
+update_post_meta($order_id, '_tracking_provider', 'JNE');
+```
+
+**Plugin registers fields for WooNooW (optional, for better UX):**
+```php
+// In plugin's main file or init hook
+add_action('woonoow/register_meta_fields', function() {
+    // Register tracking number field
+    \WooNooW\Compat\MetaFieldsRegistry::register_order_field('_tracking_number', [
+        'label' => __('Tracking Number', 'your-plugin'),
+        'type' => 'text',
+        'section' => 'Shipment Tracking',
+        'description' => 'Enter the shipment tracking number',
+        'placeholder' => 'e.g., 1234567890',
+    ]);
+    
+    // Register tracking provider field
+    \WooNooW\Compat\MetaFieldsRegistry::register_order_field('_tracking_provider', [
+        'label' => __('Tracking Provider', 'your-plugin'),
+        'type' => 'select',
+        'section' => 'Shipment Tracking',
+        'options' => [
+            ['value' => 'jne', 'label' => 'JNE'],
+            ['value' => 'jnt', 'label' => 'J&T Express'],
+            ['value' => 'sicepat', 'label' => 'SiCepat'],
+            ['value' => 'anteraja', 'label' => 'AnterAja'],
+        ],
+    ]);
+});
+```
+
+**Result:**
+- ✅ Fields automatically exposed in API
+- ✅ Fields displayed in WooNooW order edit page
+- ✅ Fields editable by admin
+- ✅ Data saved to WooCommerce database
+- ✅ Compatible with classic admin
+- ✅ **Zero migration needed**
+
+### Example 2: Advanced Custom Fields (ACF)
+
+**ACF stores data (standard way):**
+```php
+// ACF automatically stores to post meta
+update_field('custom_field', 'value', $product_id);
+// Stored as: update_post_meta($product_id, 'custom_field', 'value');
+```
+
+**Register for WooNooW (optional):**
+```php
+add_action('woonoow/register_meta_fields', function() {
+    \WooNooW\Compat\MetaFieldsRegistry::register_product_field('custom_field', [
+        'label' => __('Custom Field', 'your-plugin'),
+        'type' => 'textarea',
+        'section' => 'Custom Fields',
+    ]);
+});
+```
+
+**Result:**
+- ✅ ACF data visible in WooNooW
+- ✅ Editable in WooNooW admin
+- ✅ Synced with ACF
+- ✅ Works with both admins
+
+### Example 3: Custom Plugin (No Registration)
+
+**Plugin stores data:**
+```php
+// Plugin stores public meta (no underscore)
+update_post_meta($order_id, 'custom_note', 'Some note');
+```
+
+**Result:**
+- ✅ **Automatically exposed** (public meta)
+- ✅ Displayed in API response
+- ✅ No registration needed
+- ✅ Works immediately
+
+---
+
+## API Response Examples
+
+### Order with Meta Fields
+
+**Request:**
+```
+GET /wp-json/woonoow/v1/orders/123
+```
+
+**Response:**
+```json
+{
+  "id": 123,
+  "status": "processing",
+  "billing": {...},
+  "shipping": {...},
+  "items": [...],
+  "meta": {
+    "_tracking_number": "1234567890",
+    "_tracking_provider": "jne",
+    "custom_note": "Some note"
+  }
+}
+```
+
+### Product with Meta Fields
+
+**Request:**
+```
+GET /wp-json/woonoow/v1/products/456
+```
+
+**Response:**
+```json
+{
+  "id": 456,
+  "name": "Product Name",
+  "price": 100000,
+  "meta": {
+    "custom_field": "Custom value",
+    "another_field": "Another value"
+  }
+}
+```
+
+---
+
+## Field Types Reference
+
+### Text Field
+```php
+MetaFieldsRegistry::register_order_field('_field_name', [
+    'label' => 'Field Label',
+    'type' => 'text',
+    'placeholder' => 'Enter value...',
+]);
+```
+
+### Textarea Field
+```php
+MetaFieldsRegistry::register_order_field('_field_name', [
+    'label' => 'Field Label',
+    'type' => 'textarea',
+    'placeholder' => 'Enter description...',
+]);
+```
+
+### Number Field
+```php
+MetaFieldsRegistry::register_order_field('_field_name', [
+    'label' => 'Field Label',
+    'type' => 'number',
+    'placeholder' => '0',
+]);
+```
+
+### Select Field
+```php
+MetaFieldsRegistry::register_order_field('_field_name', [
+    'label' => 'Field Label',
+    'type' => 'select',
+    'options' => [
+        ['value' => 'option1', 'label' => 'Option 1'],
+        ['value' => 'option2', 'label' => 'Option 2'],
+    ],
+]);
+```
+
+### Date Field
+```php
+MetaFieldsRegistry::register_order_field('_field_name', [
+    'label' => 'Field Label',
+    'type' => 'date',
+]);
+```
+
+### Checkbox Field
+```php
+MetaFieldsRegistry::register_order_field('_field_name', [
+    'label' => 'Field Label',
+    'type' => 'checkbox',
+    'placeholder' => 'Enable this option',
+]);
+```
+
+---
+
+## Summary
+
+**For Plugin Developers:**
+1. ✅ Continue using standard WP/WooCommerce meta storage
+2. ✅ Optionally register fields for better UX
+3. ✅ No special integration needed
+4. ✅ Works with both classic and WooNooW admin
+
+**For WooNooW Core:**
+1. ✅ Zero addon dependencies
+2. ✅ Provides mechanism, not integration
+3. ✅ Plugins register themselves
+4. ✅ Clean separation of concerns
+
+**Result:**
+✅ **Level 1 compatibility fully implemented**
+✅ **Plugins work automatically**
+✅ **No migration needed**
+✅ **Production ready**

includes/Compat/MetaFieldsRegistry.php

@@ -0,0 +1,212 @@
+<?php
+namespace WooNooW\Compat;
+
+/**
+ * MetaFieldsRegistry
+ * 
+ * Allows plugins to register custom meta fields for display in WooNooW admin.
+ * Part of Level 1 compatibility - plugins using standard WP/WooCommerce meta
+ * storage can register their fields to be displayed automatically.
+ * 
+ * Zero coupling with specific plugins - just provides the mechanism.
+ * 
+ * @package WooNooW\Compat
+ */
+class MetaFieldsRegistry {
+	
+	/**
+	 * Registered order meta fields
+	 * @var array
+	 */
+	private static $order_fields = [];
+	
+	/**
+	 * Registered product meta fields
+	 * @var array
+	 */
+	private static $product_fields = [];
+	
+	/**
+	 * Initialize the registry
+	 */
+	public static function init() {
+		// Allow plugins to register their meta fields
+		add_action('init', [__CLASS__, 'trigger_registration'], 20);
+		
+		// Localize fields to JavaScript
+		add_action('admin_enqueue_scripts', [__CLASS__, 'localize_fields']);
+	}
+	
+	/**
+	 * Trigger the registration action for plugins
+	 */
+	public static function trigger_registration() {
+		/**
+		 * Fires when plugins can register their meta fields
+		 * 
+		 * @since 1.0.0
+		 * 
+		 * @example
+		 * add_action('woonoow/register_meta_fields', function() {
+		 *     \WooNooW\Compat\MetaFieldsRegistry::register_order_field('_tracking_number', [
+		 *         'label' => __('Tracking Number'),
+		 *         'type' => 'text',
+		 *         'section' => 'Shipment Tracking',
+		 *     ]);
+		 * });
+		 */
+		do_action('woonoow/register_meta_fields');
+	}
+	
+	/**
+	 * Register an order meta field
+	 * 
+	 * @param string $key Meta key (e.g., '_tracking_number')
+	 * @param array $args Field configuration
+	 *   - label: string - Field label (default: formatted key)
+	 *   - type: string - Field type: text, textarea, number, select, date, checkbox (default: text)
+	 *   - section: string - Section name for grouping (default: 'Additional Fields')
+	 *   - description: string - Help text (default: '')
+	 *   - placeholder: string - Placeholder text (default: '')
+	 *   - options: array - For select type: [{value: 'x', label: 'X'}] (default: [])
+	 */
+	public static function register_order_field($key, $args = []) {
+		$defaults = [
+			'key' => $key,
+			'label' => self::format_label($key),
+			'type' => 'text',
+			'section' => 'Additional Fields',
+			'description' => '',
+			'placeholder' => '',
+			'options' => [],
+		];
+		
+		self::$order_fields[$key] = array_merge($defaults, $args);
+		
+		// Auto-add to allowed meta lists (Level 1 compatibility)
+		self::add_to_allowed_meta('order', $key);
+	}
+	
+	/**
+	 * Register a product meta field
+	 * 
+	 * @param string $key Meta key (e.g., '_custom_field')
+	 * @param array $args Field configuration (same as register_order_field)
+	 */
+	public static function register_product_field($key, $args = []) {
+		$defaults = [
+			'key' => $key,
+			'label' => self::format_label($key),
+			'type' => 'text',
+			'section' => 'Additional Fields',
+			'description' => '',
+			'placeholder' => '',
+			'options' => [],
+		];
+		
+		self::$product_fields[$key] = array_merge($defaults, $args);
+		
+		// Auto-add to allowed meta lists (Level 1 compatibility)
+		self::add_to_allowed_meta('product', $key);
+	}
+	
+	/**
+	 * Format meta key to human-readable label
+	 * 
+	 * @param string $key Meta key
+	 * @return string Formatted label
+	 */
+	private static function format_label($key) {
+		// Remove leading underscore
+		$label = ltrim($key, '_');
+		
+		// Replace underscores with spaces
+		$label = str_replace('_', ' ', $label);
+		
+		// Capitalize words
+		$label = ucwords($label);
+		
+		return $label;
+	}
+	
+	/**
+	 * Add meta key to allowed lists automatically
+	 * 
+	 * @param string $type 'order' or 'product'
+	 * @param string $key Meta key
+	 */
+	private static function add_to_allowed_meta($type, $key) {
+		if ($type === 'order') {
+			// Add to allowed private meta (for reading)
+			add_filter('woonoow/order_allowed_private_meta', function($allowed) use ($key) {
+				if (!in_array($key, $allowed, true)) {
+					$allowed[] = $key;
+				}
+				return $allowed;
+			});
+			
+			// Add to updatable meta (for writing)
+			add_filter('woonoow/order_updatable_meta', function($allowed) use ($key) {
+				if (!in_array($key, $allowed, true)) {
+					$allowed[] = $key;
+				}
+				return $allowed;
+			});
+		} elseif ($type === 'product') {
+			// Add to allowed private meta (for reading)
+			add_filter('woonoow/product_allowed_private_meta', function($allowed) use ($key) {
+				if (!in_array($key, $allowed, true)) {
+					$allowed[] = $key;
+				}
+				return $allowed;
+			});
+			
+			// Add to updatable meta (for writing)
+			add_filter('woonoow/product_updatable_meta', function($allowed) use ($key) {
+				if (!in_array($key, $allowed, true)) {
+					$allowed[] = $key;
+				}
+				return $allowed;
+			});
+		}
+	}
+	
+	/**
+	 * Localize fields to JavaScript
+	 * Exposes registered fields to frontend via window.WooNooWMetaFields
+	 */
+	public static function localize_fields() {
+		// Only on admin pages
+		if (!is_admin()) {
+			return;
+		}
+		
+		// Allow plugins to modify fields before localizing
+		$order_fields = apply_filters('woonoow/meta_fields_orders', array_values(self::$order_fields));
+		$product_fields = apply_filters('woonoow/meta_fields_products', array_values(self::$product_fields));
+		
+		// Localize to JavaScript
+		wp_localize_script('woonoow-admin', 'WooNooWMetaFields', [
+			'orders' => $order_fields,
+			'products' => $product_fields,
+		]);
+	}
+	
+	/**
+	 * Get registered order fields (for testing/debugging)
+	 * 
+	 * @return array
+	 */
+	public static function get_order_fields() {
+		return self::$order_fields;
+	}
+	
+	/**
+	 * Get registered product fields (for testing/debugging)
+	 * 
+	 * @return array
+	 */
+	public static function get_product_fields() {
+		return self::$product_fields;
+	}
+}

includes/Core/Bootstrap.php

@@ -12,6 +12,7 @@ use WooNooW\Compat\RouteRegistry;
 use WooNooW\Compat\NavigationRegistry;
 use WooNooW\Compat\PaymentChannels;
 use WooNooW\Compat\SettingsProvider;
+use WooNooW\Compat\MetaFieldsRegistry;
 use WooNooW\Admin\Rest\MenuController;
 use WooNooW\Admin\Rest\SettingsController;
 use WooNooW\Api\Routes;
@@ -45,6 +46,9 @@ class Bootstrap {
         NavigationRegistry::init();
         PaymentChannels::init();
         
+        // Level 1 compatibility: Meta fields registry
+        MetaFieldsRegistry::init();
+        
         MenuProvider::init();
         MenuController::init();
         SettingsProvider::init();