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>

tests/integration/api/v1/admin/test_admin_users.py

@@ -147,7 +147,7 @@ class TestAdminUsersPlatformAssignmentAPI:
         self, client, super_admin_headers, db, test_platform_admin, test_platform, test_super_admin
     ):
         """Test removing an admin from a platform."""
-        from models.database.admin_platform import AdminPlatform
+        from app.modules.tenancy.models import AdminPlatform
 
         # First create an assignment
         assignment = AdminPlatform(
@@ -172,7 +172,7 @@ class TestAdminUsersPlatformAssignmentAPI:
         self, client, super_admin_headers, db, test_platform_admin, test_platform, test_super_admin
     ):
         """Test getting platforms for an admin."""
-        from models.database.admin_platform import AdminPlatform
+        from app.modules.tenancy.models import AdminPlatform
 
         # Create assignment
         assignment = AdminPlatform(
@@ -220,7 +220,7 @@ class TestAdminUsersSuperAdminToggleAPI:
         self, client, super_admin_headers, db, auth_manager
     ):
         """Test demoting a super admin to platform admin."""
-        from models.database.user import User
+        from app.modules.tenancy.models import User
 
         # Create another super admin to demote
         another_super = User(
@@ -270,7 +270,7 @@ class TestAdminAuthPlatformSelectionAPI:
         self, client, db, test_platform_admin, test_platform, test_super_admin, auth_manager
     ):
         """Test getting accessible platforms as platform admin."""
-        from models.database.admin_platform import AdminPlatform
+        from app.modules.tenancy.models import AdminPlatform
 
         # Create assignment
         assignment = AdminPlatform(
@@ -310,7 +310,7 @@ class TestAdminAuthPlatformSelectionAPI:
         self, client, db, test_platform_admin, test_platform, test_super_admin
     ):
         """Test selecting a platform as platform admin."""
-        from models.database.admin_platform import AdminPlatform
+        from app.modules.tenancy.models import AdminPlatform
 
         # Create assignment
         assignment = AdminPlatform(