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/checkout/routes/api/storefront.py

@@ -18,7 +18,7 @@ from sqlalchemy.orm import Session
 
 from app.api.deps import get_current_customer_api
 from app.core.database import get_db
-from app.exceptions import VendorNotFoundException
+from app.modules.tenancy.exceptions import VendorNotFoundException
 from app.modules.cart.services import cart_service
 from app.modules.checkout.schemas import (
     CheckoutRequest,
@@ -28,7 +28,7 @@ from app.modules.checkout.schemas import (
 from app.modules.checkout.services import checkout_service
 from app.modules.customers.schemas import CustomerContext
 from app.modules.orders.services import order_service
-from app.services.email_service import EmailService  # noqa: MOD-004 - Core email service
+from app.modules.messaging.services.email_service import EmailService  # noqa: MOD-004 - Core email service
 from middleware.vendor_context import require_vendor_context
 from models.database.vendor import Vendor
 from app.modules.orders.schemas import OrderCreate, OrderResponse

app/modules/checkout/routes/pages/__init__.py

@@ -0,0 +1,2 @@
+# app/modules/checkout/routes/pages/__init__.py
+"""Checkout module page routes."""

app/modules/checkout/routes/pages/storefront.py

@@ -0,0 +1,46 @@
+# app/modules/checkout/routes/pages/storefront.py
+"""
+Checkout Storefront Page Routes (HTML rendering).
+
+Storefront (customer shop) pages for checkout:
+- Checkout page
+"""
+
+import logging
+
+from fastapi import APIRouter, Depends, Request
+from fastapi.responses import HTMLResponse
+from sqlalchemy.orm import Session
+
+from app.api.deps import get_db
+from app.modules.core.utils.page_context import get_storefront_context
+from app.templates_config import templates
+
+logger = logging.getLogger(__name__)
+
+router = APIRouter()
+
+
+# ============================================================================
+# CHECKOUT
+# ============================================================================
+
+
+@router.get("/checkout", response_class=HTMLResponse, include_in_schema=False)
+async def shop_checkout_page(request: Request, db: Session = Depends(get_db)):
+    """
+    Render checkout page.
+    Handles shipping, payment, and order confirmation.
+    """
+    logger.debug(
+        "[STOREFRONT] shop_checkout_page REACHED",
+        extra={
+            "path": request.url.path,
+            "vendor": getattr(request.state, "vendor", "NOT SET"),
+            "context": getattr(request.state, "context_type", "NOT SET"),
+        },
+    )
+
+    return templates.TemplateResponse(
+        "checkout/storefront/checkout.html", get_storefront_context(request, db=db)
+    )