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/tenancy/services/admin_service.py

@@ -32,13 +32,13 @@ from app.modules.tenancy.exceptions import (
     VendorVerificationException,
 )
 from middleware.auth import AuthManager
-from models.database.company import Company
+from app.modules.tenancy.models import Company
 from app.modules.marketplace.models import MarketplaceImportJob
-from models.database.platform import Platform
-from models.database.user import User
-from models.database.vendor import Role, Vendor
+from app.modules.tenancy.models import Platform
+from app.modules.tenancy.models import User
+from app.modules.tenancy.models import Role, Vendor
 from app.modules.marketplace.schemas import MarketplaceImportJobResponse
-from models.schema.vendor import VendorCreate
+from app.modules.tenancy.schemas.vendor import VendorCreate
 
 logger = logging.getLogger(__name__)
 
@@ -422,7 +422,7 @@ class AdminService:
 
             # Assign vendor to platforms if provided
             if vendor_data.platform_ids:
-                from models.database.vendor_platform import VendorPlatform
+                from app.modules.tenancy.models import VendorPlatform
 
                 for platform_id in vendor_data.platform_ids:
                     # Verify platform exists