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/billing/services/__init__.py

@@ -27,6 +27,21 @@ from app.modules.billing.services.billing_service import (
     NoActiveSubscriptionError,
     SubscriptionNotCancelledError,
 )
+from app.modules.billing.services.feature_service import (
+    FeatureService,
+    feature_service,
+    FeatureInfo,
+    FeatureUpgradeInfo,
+    FeatureCode,
+)
+from app.modules.billing.services.capacity_forecast_service import (
+    CapacityForecastService,
+    capacity_forecast_service,
+)
+from app.modules.billing.services.platform_pricing_service import (
+    PlatformPricingService,
+    platform_pricing_service,
+)
 
 __all__ = [
     "SubscriptionService",
@@ -43,4 +58,13 @@ __all__ = [
     "StripePriceNotConfiguredError",
     "NoActiveSubscriptionError",
     "SubscriptionNotCancelledError",
+    "FeatureService",
+    "feature_service",
+    "FeatureInfo",
+    "FeatureUpgradeInfo",
+    "FeatureCode",
+    "CapacityForecastService",
+    "capacity_forecast_service",
+    "PlatformPricingService",
+    "platform_pricing_service",
 ]