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/schema/__init__.py

@@ -1,23 +1,30 @@
 # models/schema/__init__.py
-"""API models package - Pydantic models for request/response validation.
+"""API models package - Base classes only.
 
-Note: Many schemas have been migrated to their respective modules:
+This package provides the base infrastructure for Pydantic schemas:
+- BaseModel configuration
+- Common response patterns
+- Auth schemas (cross-cutting)
+
+IMPORTANT: Domain schemas have been migrated to their respective modules:
+- Tenancy schemas: app.modules.tenancy.schemas
+- CMS schemas: app.modules.cms.schemas
+- Messaging schemas: app.modules.messaging.schemas
 - Customer schemas: app.modules.customers.schemas
 - Order schemas: app.modules.orders.schemas
 - Inventory schemas: app.modules.inventory.schemas
-- Message schemas: app.modules.messaging.schemas
 - Cart schemas: app.modules.cart.schemas
 - Marketplace schemas: app.modules.marketplace.schemas
 - Catalog/Product schemas: app.modules.catalog.schemas
 - Payment schemas: app.modules.payments.schemas
+
+Import schemas from their canonical module locations instead of this package.
 """
 
-# Import API model modules that remain in legacy location
+# Infrastructure schemas that remain here
 from . import (
     auth,
     base,
-    email,
-    vendor,
 )
 
 # Common imports for convenience
@@ -26,6 +33,4 @@ from .base import *  # Base Pydantic models
 __all__ = [
     "base",
     "auth",
-    "email",
-    "vendor",
 ]