refactor: migrate templates and static files to self-contained modules

Templates Migration:
- Migrate admin templates to modules (tenancy, billing, monitoring, marketplace, etc.)
- Migrate vendor templates to modules (tenancy, billing, orders, messaging, etc.)
- Migrate storefront templates to modules (catalog, customers, orders, cart, checkout, cms)
- Migrate public templates to modules (billing, marketplace, cms)
- Keep shared templates in app/templates/ (base.html, errors/, partials/, macros/)
- Migrate letzshop partials to marketplace module

Static Files Migration:
- Migrate admin JS to modules: tenancy (23 files), core (5 files), monitoring (1 file)
- Migrate vendor JS to modules: tenancy (4 files), core (2 files)
- Migrate shared JS: vendor-selector.js to core, media-picker.js to cms
- Migrate storefront JS: storefront-layout.js to core
- Keep framework JS in static/ (api-client, utils, money, icons, log-config, lib/)
- Update all template references to use module_static paths

Naming Consistency:
- Rename static/platform/ to static/public/
- Rename app/templates/platform/ to app/templates/public/
- Update all extends and static references

Documentation:
- Update module-system.md with shared templates documentation
- Update frontend-structure.md with new module JS organization

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

app/modules/analytics/services/stats_service.py

@@ -18,7 +18,7 @@ from typing import Any
 from sqlalchemy import func
 from sqlalchemy.orm import Session
 
-from app.exceptions import AdminOperationException, VendorNotFoundException
+from app.modules.tenancy.exceptions import AdminOperationException, VendorNotFoundException
 from app.modules.customers.models.customer import Customer
 from app.modules.inventory.models import Inventory
 from app.modules.marketplace.models import MarketplaceImportJob, MarketplaceProduct

app/modules/analytics/services/usage_service.py

@@ -93,7 +93,7 @@ class UsageService:
 
         Returns current usage, limits, and upgrade recommendations.
         """
-        from app.services.subscription_service import subscription_service
+        from app.modules.billing.services.subscription_service import subscription_service
 
         # Get subscription
         subscription = subscription_service.get_or_create_subscription(db, vendor_id)
@@ -151,7 +151,7 @@ class UsageService:
         Returns:
             LimitCheckData with proceed status and upgrade info
         """
-        from app.services.subscription_service import subscription_service
+        from app.modules.billing.services.subscription_service import subscription_service
 
         if limit_type == "orders":
             can_proceed, message = subscription_service.can_create_order(db, vendor_id)