feat: Add backend API endpoints for taxonomy CRUD operations

Problem: Frontend taxonomy pages (Categories, Tags, Attributes) were getting 404 errors
when trying to create/update/delete because the backend endpoints didn't exist.

Solution: Added complete CRUD API endpoints to ProductsController

Routes Added:
1. Categories:
   - POST   /products/categories (create)
   - PUT    /products/categories/{id} (update)
   - DELETE /products/categories/{id} (delete)

2. Tags:
   - POST   /products/tags (create)
   - PUT    /products/tags/{id} (update)
   - DELETE /products/tags/{id} (delete)

3. Attributes:
   - POST   /products/attributes (create)
   - PUT    /products/attributes/{id} (update)
   - DELETE /products/attributes/{id} (delete)

Implementation:
- All endpoints use admin permission check
- Proper sanitization of inputs
- WordPress taxonomy functions (wp_insert_term, wp_update_term, wp_delete_term)
- WooCommerce attribute functions (wc_create_attribute, wc_update_attribute, wc_delete_attribute)
- Error handling with WP_Error checks
- Consistent response format with success/data/message

Methods Added:
- create_category() / update_category() / delete_category()
- create_tag() / update_tag() / delete_tag()
- create_attribute() / update_attribute() / delete_attribute()

Files Modified:
- includes/Api/ProductsController.php (added 9 CRUD methods + route registrations)

Result:
✅ Categories can now be created/edited/deleted from admin SPA
✅ Tags can now be created/edited/deleted from admin SPA
✅ Attributes can now be created/edited/deleted from admin SPA
✅ No more 404 errors on taxonomy operations

includes/Api/ProductsController.php

@@ -123,6 +123,69 @@ class ProductsController {
 			'callback' => [__CLASS__, 'get_attributes'],
 			'permission_callback' => [Permissions::class, 'check_admin_permission'],
 		]);
+		
+		// Create category
+		register_rest_route('woonoow/v1', '/products/categories', [
+			'methods' => 'POST',
+			'callback' => [__CLASS__, 'create_category'],
+			'permission_callback' => [Permissions::class, 'check_admin_permission'],
+		]);
+		
+		// Update category
+		register_rest_route('woonoow/v1', '/products/categories/(?P<id>\d+)', [
+			'methods' => 'PUT',
+			'callback' => [__CLASS__, 'update_category'],
+			'permission_callback' => [Permissions::class, 'check_admin_permission'],
+		]);
+		
+		// Delete category
+		register_rest_route('woonoow/v1', '/products/categories/(?P<id>\d+)', [
+			'methods' => 'DELETE',
+			'callback' => [__CLASS__, 'delete_category'],
+			'permission_callback' => [Permissions::class, 'check_admin_permission'],
+		]);
+		
+		// Create tag
+		register_rest_route('woonoow/v1', '/products/tags', [
+			'methods' => 'POST',
+			'callback' => [__CLASS__, 'create_tag'],
+			'permission_callback' => [Permissions::class, 'check_admin_permission'],
+		]);
+		
+		// Update tag
+		register_rest_route('woonoow/v1', '/products/tags/(?P<id>\d+)', [
+			'methods' => 'PUT',
+			'callback' => [__CLASS__, 'update_tag'],
+			'permission_callback' => [Permissions::class, 'check_admin_permission'],
+		]);
+		
+		// Delete tag
+		register_rest_route('woonoow/v1', '/products/tags/(?P<id>\d+)', [
+			'methods' => 'DELETE',
+			'callback' => [__CLASS__, 'delete_tag'],
+			'permission_callback' => [Permissions::class, 'check_admin_permission'],
+		]);
+		
+		// Create attribute
+		register_rest_route('woonoow/v1', '/products/attributes', [
+			'methods' => 'POST',
+			'callback' => [__CLASS__, 'create_attribute'],
+			'permission_callback' => [Permissions::class, 'check_admin_permission'],
+		]);
+		
+		// Update attribute
+		register_rest_route('woonoow/v1', '/products/attributes/(?P<id>\d+)', [
+			'methods' => 'PUT',
+			'callback' => [__CLASS__, 'update_attribute'],
+			'permission_callback' => [Permissions::class, 'check_admin_permission'],
+		]);
+		
+		// Delete attribute
+		register_rest_route('woonoow/v1', '/products/attributes/(?P<id>\d+)', [
+			'methods' => 'DELETE',
+			'callback' => [__CLASS__, 'delete_attribute'],
+			'permission_callback' => [Permissions::class, 'check_admin_permission'],
+		]);
 	}
 	
 	/**