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/customers/routes/api/storefront.py

@@ -23,14 +23,15 @@ from sqlalchemy.orm import Session
 from app.api.deps import get_current_customer_api
 from app.core.database import get_db
 from app.core.environment import should_use_secure_cookies
-from app.exceptions import ValidationException, VendorNotFoundException
+from app.exceptions import ValidationException
+from app.modules.tenancy.exceptions import VendorNotFoundException
 from app.modules.customers.schemas import CustomerContext
 from app.modules.customers.services import (
     customer_address_service,
     customer_service,
 )
-from app.services.auth_service import AuthService  # noqa: MOD-004 - Core auth service
-from app.services.email_service import EmailService  # noqa: MOD-004 - Core email service
+from app.modules.core.services.auth_service import AuthService  # noqa: MOD-004 - Core auth service
+from app.modules.messaging.services.email_service import EmailService  # noqa: MOD-004 - Core email service
 from app.modules.customers.models import PasswordResetToken
 from models.schema.auth import (
     LogoutResponse,