refactor: clean up legacy models and migrate remaining schemas

Delete empty stub files from models/database/:
- audit.py, backup.py, configuration.py, monitoring.py
- notification.py, payment.py, search.py, task.py

Delete re-export files:
- models/database/subscription.py → app.modules.billing.models
- models/database/architecture_scan.py → app.modules.dev_tools.models
- models/database/test_run.py → app.modules.dev_tools.models
- models/schema/subscription.py → app.modules.billing.schemas
- models/schema/marketplace.py (empty)
- models/schema/monitoring.py (empty)

Migrate schemas to canonical module locations:
- billing.py → app/modules/billing/schemas/
- vendor_product.py → app/modules/catalog/schemas/
- homepage_sections.py → app/modules/cms/schemas/

Keep as CORE (framework-level, used everywhere):
- models/schema/: admin, auth, base, company, email, image, media, team, vendor*
- models/database/: admin*, base, company, email, feature, media, platform*, user, vendor*

Update 30+ files to use canonical import locations.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

models/database/__init__.py

@@ -32,7 +32,7 @@ from .admin import (
 from app.modules.messaging.models import AdminNotification
 from .admin_menu_config import AdminMenuConfig, FrontendType, MANDATORY_MENU_ITEMS
 from .admin_platform import AdminPlatform
-from .architecture_scan import (
+from app.modules.dev_tools.models import (
     ArchitectureScan,
     ArchitectureViolation,
     ViolationAssignment,
@@ -82,7 +82,7 @@ from app.modules.marketplace.models import OnboardingStatus, OnboardingStep, Ven
 from app.modules.orders.models import Order, OrderItem
 from app.modules.orders.models import OrderItemException
 from app.modules.catalog.models import Product, ProductTranslation
-from .subscription import (
+from app.modules.billing.models import (
     AddOnCategory,
     AddOnProduct,
     BillingHistory,
@@ -95,7 +95,7 @@ from .subscription import (
     VendorAddOn,
     VendorSubscription,
 )
-from .test_run import TestCollection, TestResult, TestRun
+from app.modules.dev_tools.models import TestCollection, TestResult, TestRun
 from .user import User
 from .vendor import Role, Vendor, VendorUser
 from .vendor_domain import VendorDomain