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/cms/models/__init__.py

@@ -2,19 +2,24 @@
 """
 CMS module database models.
 
-This is the canonical location for CMS models. Module models are automatically
-discovered and registered with SQLAlchemy's Base.metadata at startup.
+This is the canonical location for CMS models including:
+- ContentPage: CMS pages (marketing, vendor default pages)
+- MediaFile: Vendor media library
+- VendorTheme: Vendor storefront theme configuration
 
 Usage:
-    from app.modules.cms.models import ContentPage
+    from app.modules.cms.models import ContentPage, MediaFile, VendorTheme
 
-For media models:
-    from models.database.media import MediaFile  # Core media file storage
-    from app.modules.catalog.models import ProductMedia  # Product-media associations
+For product-media associations:
+    from app.modules.catalog.models import ProductMedia
 """
 
 from app.modules.cms.models.content_page import ContentPage
+from app.modules.cms.models.media import MediaFile
+from app.modules.cms.models.vendor_theme import VendorTheme
 
 __all__ = [
     "ContentPage",
+    "MediaFile",
+    "VendorTheme",
 ]