refactor: complete module-driven architecture migration

This commit completes the migration to a fully module-driven architecture:

## Models Migration
- Moved all domain models from models/database/ to their respective modules:
  - tenancy: User, Admin, Vendor, Company, Platform, VendorDomain, etc.
  - cms: MediaFile, VendorTheme
  - messaging: Email, VendorEmailSettings, VendorEmailTemplate
  - core: AdminMenuConfig
- models/database/ now only contains Base and TimestampMixin (infrastructure)

## Schemas Migration
- Moved all domain schemas from models/schema/ to their respective modules:
  - tenancy: company, vendor, admin, team, vendor_domain
  - cms: media, image, vendor_theme
  - messaging: email
- models/schema/ now only contains base.py and auth.py (infrastructure)

## Routes Migration
- Moved admin routes from app/api/v1/admin/ to modules:
  - menu_config.py -> core module
  - modules.py -> tenancy module
  - module_config.py -> tenancy module
- app/api/v1/admin/ now only aggregates auto-discovered module routes

## Menu System
- Implemented module-driven menu system with MenuDiscoveryService
- Extended FrontendType enum: PLATFORM, ADMIN, VENDOR, STOREFRONT
- Added MenuItemDefinition and MenuSectionDefinition dataclasses
- Each module now defines its own menu items in definition.py
- MenuService integrates with MenuDiscoveryService for template rendering

## Documentation
- Updated docs/architecture/models-structure.md
- Updated docs/architecture/menu-management.md
- Updated architecture validation rules for new exceptions

## Architecture Validation
- Updated MOD-019 rule to allow base.py in models/schema/
- Created core module exceptions.py and schemas/ directory
- All validation errors resolved (only warnings remain)

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

app/modules/billing/static/vendor/js/billing.js

@@ -29,6 +29,9 @@ function vendorBilling() {
 
         // Initialize
         async init() {
+            // Load i18n translations
+            await I18n.loadModule('billing');
+
             // Guard against multiple initialization
             if (window._vendorBillingInitialized) return;
             window._vendorBillingInitialized = true;
@@ -81,7 +84,7 @@ function vendorBilling() {
 
             } catch (error) {
                 billingLog.error('Error loading billing data:', error);
-                Utils.showToast('Failed to load billing data', 'error');
+                Utils.showToast(I18n.t('billing.messages.failed_to_load_billing_data'), 'error');
             } finally {
                 this.loading = false;
             }
@@ -101,7 +104,7 @@ function vendorBilling() {
                 }
             } catch (error) {
                 billingLog.error('Error creating checkout:', error);
-                Utils.showToast('Failed to create checkout session', 'error');
+                Utils.showToast(I18n.t('billing.messages.failed_to_create_checkout_session'), 'error');
             }
         },
 
@@ -113,7 +116,7 @@ function vendorBilling() {
                 }
             } catch (error) {
                 billingLog.error('Error opening portal:', error);
-                Utils.showToast('Failed to open payment portal', 'error');
+                Utils.showToast(I18n.t('billing.messages.failed_to_open_payment_portal'), 'error');
             }
         },
 
@@ -125,24 +128,24 @@ function vendorBilling() {
                 });
 
                 this.showCancelModal = false;
-                Utils.showToast('Subscription cancelled. You have access until the end of your billing period.', 'success');
+                Utils.showToast(I18n.t('billing.messages.subscription_cancelled_you_have_access_u'), 'success');
                 await this.loadData();
 
             } catch (error) {
                 billingLog.error('Error cancelling subscription:', error);
-                Utils.showToast('Failed to cancel subscription', 'error');
+                Utils.showToast(I18n.t('billing.messages.failed_to_cancel_subscription'), 'error');
             }
         },
 
         async reactivate() {
             try {
                 await apiClient.post('/vendor/billing/reactivate', {});
-                Utils.showToast('Subscription reactivated!', 'success');
+                Utils.showToast(I18n.t('billing.messages.subscription_reactivated'), 'success');
                 await this.loadData();
 
             } catch (error) {
                 billingLog.error('Error reactivating subscription:', error);
-                Utils.showToast('Failed to reactivate subscription', 'error');
+                Utils.showToast(I18n.t('billing.messages.failed_to_reactivate_subscription'), 'error');
             }
         },
 
@@ -159,7 +162,7 @@ function vendorBilling() {
                 }
             } catch (error) {
                 billingLog.error('Error purchasing addon:', error);
-                Utils.showToast('Failed to purchase add-on', 'error');
+                Utils.showToast(I18n.t('billing.messages.failed_to_purchase_addon'), 'error');
             } finally {
                 this.purchasingAddon = null;
             }
@@ -172,11 +175,11 @@ function vendorBilling() {
 
             try {
                 await apiClient.delete(`/vendor/billing/addons/${addon.id}`);
-                Utils.showToast('Add-on cancelled successfully', 'success');
+                Utils.showToast(I18n.t('billing.messages.addon_cancelled_successfully'), 'success');
                 await this.loadData();
             } catch (error) {
                 billingLog.error('Error cancelling addon:', error);
-                Utils.showToast('Failed to cancel add-on', 'error');
+                Utils.showToast(I18n.t('billing.messages.failed_to_cancel_addon'), 'error');
             }
         },