fix: store login crash and dashboard misrouted as storefront

- Seed default RBAC roles per store and assign role_id to StoreUser
  records (was never implemented after RBAC Phase 1 cleanup)
- Handle nullable role in auth_service find_user_store and
  get_user_store_role to prevent NoneType crash on login
- Use platform_clean_path instead of clean_path in FrontendTypeMiddleware
  so /store/X/dashboard is detected as STORE, not STOREFRONT

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

middleware/frontend_type.py

@@ -43,8 +43,11 @@ class FrontendTypeMiddleware(BaseHTTPMiddleware):
     async def dispatch(self, request: Request, call_next):
         """Detect frontend type and inject into request state."""
         host = request.headers.get("host", "")
-        # Use clean_path if available (from store_context_middleware), else original path
-        path = getattr(request.state, "clean_path", None) or request.url.path
+        # Use platform_clean_path (platform prefix stripped, store prefix retained)
+        # so FrontendDetector can distinguish /store/ from /storefront/.
+        # Do NOT use clean_path here — it has the store prefix stripped too,
+        # which makes /store/X/dashboard indistinguishable from /storefront/X/products.
+        path = getattr(request.state, "platform_clean_path", None) or request.url.path
 
         # Check if store context exists (set by StoreContextMiddleware)
         has_store_context = (