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>

scripts/seed_demo.py

@@ -52,8 +52,8 @@ from app.core.database import SessionLocal
 from app.core.environment import get_environment, is_production
 from middleware.auth import AuthManager
 from app.modules.cms.models import ContentPage
-from models.database.admin import PlatformAlert
-from models.database.company import Company
+from app.modules.tenancy.models import PlatformAlert
+from app.modules.tenancy.models import Company
 from app.modules.customers.models.customer import Customer, CustomerAddress
 from app.modules.marketplace.models import (
     MarketplaceImportJob,
@@ -62,10 +62,10 @@ from app.modules.marketplace.models import (
 )
 from app.modules.orders.models import Order, OrderItem
 from app.modules.catalog.models import Product
-from models.database.user import User
-from models.database.vendor import Role, Vendor, VendorUser
-from models.database.vendor_domain import VendorDomain
-from models.database.vendor_theme import VendorTheme
+from app.modules.tenancy.models import User
+from app.modules.tenancy.models import Role, Vendor, VendorUser
+from app.modules.tenancy.models import VendorDomain
+from app.modules.cms.models import VendorTheme
 
 SEED_MODE = os.getenv("SEED_MODE", "normal")  # normal, minimal, reset
 FORCE_RESET = os.getenv("FORCE_RESET", "false").lower() in ("true", "1", "yes")