feat: Complete markdown syntax refinement and variable protection

✅ New cleaner syntax implemented:
- [card:type] instead of [card type='type']
- [button:style](url)Text[/button] instead of [button url='...' style='...']
- Standard markdown images: ![alt](url)

✅ Variable protection from markdown parsing:
- Variables with underscores (e.g., {order_items_table}) now protected
- HTML comment placeholders prevent italic/bold parsing
- All variables render correctly in preview

✅ Button rendering fixes:
- Buttons work in Visual mode inside cards
- Buttons work in Preview mode
- Button clicks prevented in visual editor
- Proper styling for solid and outline buttons

✅ Backward compatibility:
- Old syntax still supported
- No breaking changes

✅ Bug fixes:
- Fixed order_item_table → order_items_table naming
- Fixed button regex to match across newlines
- Added button/image parsing to parseMarkdownBasics
- Prevented button clicks on .button and .button-outline classes

📚 Documentation:
- NEW_MARKDOWN_SYNTAX.md - Complete user guide
- MARKDOWN_SYNTAX_AND_VARIABLES.md - Technical analysis

SINGLE_SOURCE_OF_TRUTH.md

@@ -0,0 +1,162 @@
+# Single Source of Truth - Event Registry
+
+## Problem Solved
+
+Previously, events were hardcoded in multiple places:
+- ❌ `NotificationsController.php` - hardcoded 9 events
+- ❌ `TemplateProvider.php` - hardcoded 9 events  
+- ❌ `DefaultTemplates.php` - had 15 templates (8 customer + 7 staff)
+
+**Result:** Mismatches, confusion, missing templates
+
+## Solution: EventRegistry
+
+Created `/includes/Core/Notifications/EventRegistry.php` as the **SINGLE SOURCE OF TRUTH**.
+
+### How It Works
+
+```php
+// Get all events
+$events = EventRegistry::get_all_events();
+
+// Get by recipient
+$staff_events = EventRegistry::get_events_by_recipient('staff');
+$customer_events = EventRegistry::get_events_by_recipient('customer');
+
+// Get by category
+$order_events = EventRegistry::get_events_by_category('orders');
+
+// Check if exists
+if (EventRegistry::event_exists('order_placed', 'staff')) {
+    // ...
+}
+```
+
+### Current Event List
+
+**Staff Events (7):**
+1. `order_placed` - New order notification
+2. `order_processing` - Order confirmed, ready to process
+3. `order_shipped` - Order shipped
+4. `order_completed` - Order completed
+5. `order_cancelled` - Order cancelled
+6. `payment_received` - Payment confirmed
+7. `payment_failed` - Payment failed
+
+**Customer Events (8):**
+1. `order_placed` - Order placed confirmation
+2. `order_processing` - Order being processed
+3. `order_shipped` - Order shipped with tracking
+4. `order_completed` - Order delivered
+5. `order_cancelled` - Order cancelled
+6. `payment_received` - Payment confirmed
+7. `payment_failed` - Payment failed, retry
+8. `new_customer` - Welcome email
+
+**Total: 15 events** (7 staff + 8 customer)
+
+### Filter Hook
+
+```php
+add_filter('woonoow_notification_events_registry', function($events) {
+    // Add custom event
+    $events['custom_event'] = [
+        'id' => 'custom_event',
+        'label' => 'Custom Event',
+        'description' => 'My custom notification',
+        'category' => 'custom',
+        'recipient_type' => 'customer',
+        'wc_email' => '',
+        'enabled' => true,
+    ];
+    
+    return $events;
+});
+```
+
+## Components Updated
+
+### 1. NotificationsController.php
+```php
+// OLD - Hardcoded
+$events = [
+    'orders' => [
+        ['id' => 'order_placed', ...],
+        // ... 100+ lines
+    ]
+];
+
+// NEW - Uses Registry
+$all_events = EventRegistry::get_all_events();
+foreach ($all_events as $event) {
+    // Group by category
+}
+```
+
+### 2. TemplateProvider.php
+```php
+// OLD - Hardcoded
+$events = [
+    'order_placed' => 'staff',
+    'order_processing' => 'customer',
+    // ...
+];
+
+// NEW - Uses Registry
+$all_events = EventRegistry::get_all_events();
+foreach ($all_events as $event) {
+    $event_id = $event['id'];
+    $recipient_type = $event['recipient_type'];
+    // Generate templates
+}
+```
+
+### 3. DefaultTemplates.php
+**No changes needed** - Already has all 15 templates matching the registry!
+
+## Benefits
+
+✅ **Single source of truth** - One place to add/remove events
+✅ **No hardcoding** - All components query the registry
+✅ **Extensible** - Filter hook for custom events
+✅ **Type-safe** - Consistent event structure
+✅ **No mismatches** - Events and templates always aligned
+✅ **Easy maintenance** - Add event once, works everywhere
+
+## Adding New Events
+
+1. **Add to EventRegistry.php:**
+```php
+'low_stock' => [
+    'id' => 'low_stock',
+    'label' => __('Low Stock Alert', 'woonoow'),
+    'description' => __('When product stock is low', 'woonoow'),
+    'category' => 'products',
+    'recipient_type' => 'staff',
+    'wc_email' => 'low_stock',
+    'enabled' => true,
+],
+```
+
+2. **Add template to DefaultTemplates.php:**
+```php
+'staff' => [
+    // ...
+    'low_stock' => self::staff_low_stock(),
+],
+
+private static function staff_low_stock() {
+    return '[card type="warning"]...';
+}
+```
+
+3. **Done!** API and UI automatically show the new event.
+
+## Testing
+
+After refresh:
+- ✅ Events API returns 15 events (7 staff + 8 customer)
+- ✅ Templates API returns 15 templates
+- ✅ UI shows correct counts
+- ✅ All templates load without errors
+- ✅ No hardcoded lists anywhere