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>

app/services/capacity_forecast_service.py

@@ -17,7 +17,7 @@ from sqlalchemy import func
 from sqlalchemy.orm import Session
 
 from app.modules.catalog.models import Product
-from models.database.subscription import (
+from app.modules.billing.models import (
     CapacitySnapshot,
     SubscriptionStatus,
     VendorSubscription,

app/services/feature_service.py

@@ -35,7 +35,7 @@ from app.exceptions.feature import (
     TierNotFoundError,
 )
 from models.database.feature import Feature, FeatureCode
-from models.database.subscription import SubscriptionTier, VendorSubscription
+from app.modules.billing.models import SubscriptionTier, VendorSubscription
 
 logger = logging.getLogger(__name__)
 

app/services/platform_health_service.py

@@ -172,7 +172,7 @@ class PlatformHealthService:
 
         Returns aggregated limits and current usage for capacity planning.
         """
-        from models.database.subscription import VendorSubscription
+        from app.modules.billing.models import VendorSubscription
         from models.database.vendor import VendorUser
 
         # Get all active subscriptions with their limits

app/services/platform_pricing_service.py

@@ -7,7 +7,7 @@ Handles database operations for subscription tiers and add-on products.
 
 from sqlalchemy.orm import Session
 
-from models.database.subscription import (
+from app.modules.billing.models import (
     AddOnProduct,
     SubscriptionTier,
     TIER_LIMITS,

app/services/platform_signup_service.py

@@ -27,7 +27,7 @@ from app.services.onboarding_service import OnboardingService
 from app.services.stripe_service import stripe_service
 from middleware.auth import AuthManager
 from models.database.company import Company
-from models.database.subscription import (
+from app.modules.billing.models import (
     SubscriptionStatus,
     TierCode,
     TIER_LIMITS,