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/api/deps.py

@@ -51,8 +51,8 @@ from app.modules.tenancy.exceptions import (
 from app.modules.tenancy.services.vendor_service import vendor_service
 from middleware.auth import AuthManager
 from middleware.rate_limiter import RateLimiter
-from models.database.user import User as UserModel
-from models.database.vendor import Vendor
+from app.modules.tenancy.models import User as UserModel
+from app.modules.tenancy.models import Vendor
 from models.schema.auth import UserContext
 
 # Initialize dependencies
@@ -381,7 +381,7 @@ def get_admin_with_platform_context(
         InvalidTokenException: If platform admin token missing platform info
         InsufficientPermissionsException: If platform access revoked
     """
-    from models.database.platform import Platform
+    from app.modules.tenancy.models import Platform
 
     # Get raw token for platform_id extraction
     token, source = _get_token_from_request(
@@ -553,7 +553,7 @@ def require_menu_access(menu_item_id: str, frontend_type: "FrontendType"):
     from app.modules.registry import get_menu_item_module
     from app.modules.service import module_service
     from app.modules.core.services.menu_service import menu_service
-    from models.database.admin_menu_config import FrontendType as FT
+    from app.modules.enums import FrontendType as FT
 
     def _check_menu_access(
         request: Request,