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/routes/platform_pages.py

@@ -172,7 +172,7 @@ async def homepage(
         context["platform"] = platform
 
         # Include subscription tiers for pricing section
-        from models.database.subscription import TIER_LIMITS, TierCode
+        from app.modules.billing.models import TIER_LIMITS, TierCode
 
         tiers = []
         for tier_code, limits in TIER_LIMITS.items():
@@ -202,7 +202,7 @@ async def homepage(
     context["platform"] = platform
 
     # Fetch tiers for display (use API service internally)
-    from models.database.subscription import TIER_LIMITS, TierCode
+    from app.modules.billing.models import TIER_LIMITS, TierCode
 
     tiers = []
     for tier_code, limits in TIER_LIMITS.items():
@@ -276,7 +276,7 @@ async def pricing_page(
     context = get_platform_context(request, db)
 
     # Reuse tier data from homepage
-    from models.database.subscription import TIER_LIMITS, TierCode
+    from app.modules.billing.models import TIER_LIMITS, TierCode
 
     tiers = []
     for tier_code, limits in TIER_LIMITS.items():
@@ -352,7 +352,7 @@ async def signup_page(
     context["is_annual"] = annual
 
     # Get tiers for tier selection step
-    from models.database.subscription import TIER_LIMITS, TierCode
+    from app.modules.billing.models import TIER_LIMITS, TierCode
 
     tiers = []
     for tier_code, limits in TIER_LIMITS.items():