Implement multi-domain licensing for v0.5.0

- Add multi-domain checkout support for WooCommerce Blocks
- Fix domain field rendering using ExperimentalOrderMeta slot
- Add DOM injection fallback for checkout field rendering
- Update translations with new multi-domain strings (de_CH)
- Update email templates for grouped license display
- Refactor account page to group licenses by product/order

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/Admin/SettingsController.php

@@ -202,6 +202,13 @@ final class SettingsController
                 'id' => 'wc_licensed_product_default_bind_to_version',
                 'default' => 'no',
             ],
+            'enable_multi_domain' => [
+                'name' => __('Enable Multi-Domain Licensing', 'wc-licensed-product'),
+                'type' => 'checkbox',
+                'desc' => __('Allow customers to purchase multiple licenses for different domains at once. Each unit in cart quantity requires a unique domain.', 'wc-licensed-product'),
+                'id' => 'wc_licensed_product_enable_multi_domain',
+                'default' => 'no',
+            ],
             'section_end' => [
                 'type' => 'sectionend',
                 'id' => 'wc_licensed_product_section_defaults_end',
@@ -387,6 +394,14 @@ final class SettingsController
         return get_option('wc_licensed_product_default_bind_to_version', 'no') === 'yes';
     }
 
+    /**
+     * Check if multi-domain licensing is enabled
+     */
+    public static function isMultiDomainEnabled(): bool
+    {
+        return get_option('wc_licensed_product_enable_multi_domain', 'no') === 'yes';
+    }
+
     /**
      * Check if expiration warning emails are enabled
      * This checks both the WooCommerce email setting and the old setting for backwards compatibility