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>

models/__init__.py

@@ -4,24 +4,20 @@
 # API models (Pydantic) - import the modules, not all classes
 from . import schema
 
-# Database models (SQLAlchemy)
+# Database models (SQLAlchemy) - base only, avoid circular imports
 from .database.base import Base
-from .database.user import User
-from .database.vendor import Vendor
 
-# Module-based models
-from app.modules.inventory.models import Inventory
-from app.modules.marketplace.models import MarketplaceImportJob, MarketplaceProduct
-from app.modules.catalog.models import Product
+# Note: User, Vendor, and other domain models should be imported from
+# their canonical locations in app/modules/*/models/
+#
+# Example:
+#   from app.modules.tenancy.models import User, Vendor
+#   from app.modules.catalog.models import Product
+#   from app.modules.inventory.models import Inventory
+#   from app.modules.marketplace.models import MarketplaceImportJob, MarketplaceProduct
 
-# Export database models for Alembic
+# Export database base for Alembic
 __all__ = [
     "Base",
-    "User",
-    "MarketplaceProduct",
-    "Inventory",
-    "Vendor",
-    "Product",
-    "MarketplaceImportJob",
-    "api",  # API models namespace
+    "schema",  # API models namespace
 ]