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>

alembic/env.py

@@ -40,7 +40,7 @@ print("=" * 70)
 # ADMIN MODELS
 # ----------------------------------------------------------------------------
 try:
-    from models.database.admin import (
+    from app.modules.tenancy.models import (
         AdminAuditLog,
         AdminNotification,
         AdminSession,
@@ -61,7 +61,7 @@ except ImportError as e:
 # USER MODEL
 # ----------------------------------------------------------------------------
 try:
-    from models.database.user import User
+    from app.modules.tenancy.models import User
 
     print("  ✓ User model imported")
 except ImportError as e:
@@ -71,7 +71,7 @@ except ImportError as e:
 # VENDOR MODELS
 # ----------------------------------------------------------------------------
 try:
-    from models.database.vendor import Role, Vendor, VendorUser
+    from app.modules.tenancy.models import Role, Vendor, VendorUser
 
     print("  ✓ Vendor models imported (3 models)")
     print("    - Vendor")
@@ -81,14 +81,14 @@ except ImportError as e:
     print(f"  ✗ Vendor models failed: {e}")
 
 try:
-    from models.database.vendor_domain import VendorDomain
+    from app.modules.tenancy.models import VendorDomain
 
     print("  ✓ VendorDomain model imported")
 except ImportError as e:
     print(f"  ✗ VendorDomain model failed: {e}")
 
 try:
-    from models.database.vendor_theme import VendorTheme
+    from app.modules.cms.models import VendorTheme
 
     print("  ✓ VendorTheme model imported")
 except ImportError as e: