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/enums.py

@@ -21,12 +21,15 @@ import enum
 class FrontendType(str, enum.Enum):
     """Frontend types that can have menu configuration."""
 
-    ADMIN = "admin"    # Admin panel (super admins, platform admins)
-    VENDOR = "vendor"  # Vendor dashboard
+    PLATFORM = "platform"    # Public marketing pages (pricing, signup, about)
+    ADMIN = "admin"          # Admin panel (super admins, platform admins)
+    VENDOR = "vendor"        # Vendor dashboard
+    STOREFRONT = "storefront"  # Customer-facing shop
 
 
 # Menu items that cannot be hidden - always visible regardless of config
 # Organized by frontend type
+# NOTE: This will be deprecated in favor of MenuItemDefinition.is_mandatory
 MANDATORY_MENU_ITEMS = {
     FrontendType.ADMIN: frozenset({
         "dashboard",  # Default landing page after login
@@ -40,6 +43,8 @@ MANDATORY_MENU_ITEMS = {
         "dashboard",  # Default landing page after login
         "settings",
     }),
+    FrontendType.PLATFORM: frozenset(),
+    FrontendType.STOREFRONT: frozenset(),
 }