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>

tests/unit/services/test_order_service.py

@@ -16,12 +16,10 @@ from unittest.mock import MagicMock, patch
 
 import pytest
 
-from app.exceptions import (
-    CustomerNotFoundException,
-    OrderNotFoundException,
-    ValidationException,
-)
-from app.services.order_service import (
+from app.exceptions import ValidationException
+from app.modules.customers.exceptions import CustomerNotFoundException
+from app.modules.orders.exceptions import OrderNotFoundException
+from app.modules.orders.services.order_service import (
     PLACEHOLDER_GTIN,
     PLACEHOLDER_MARKETPLACE_ID,
     OrderService,
@@ -518,7 +516,7 @@ class TestOrderServiceLetzshop:
         }
 
         with patch(
-            "app.services.order_service.subscription_service"
+            "app.modules.orders.services.order_service.subscription_service"
         ) as mock_sub:
             mock_sub.can_create_order.return_value = (True, None)
             mock_sub.increment_order_count.return_value = None