Initial KDS scaffold — Phase 2 kitchen port

FastAPI backend (Python 3.11, httpx for SignalR/GraphQL — no MSSQL ODBC),
shares kitchen_db directly. React/TS/Vite fullscreen board frontend.

Backend: auth.py (APP_SLUG=kds, SimpleNamespace), main.py (4 KDS migrations,
SignalR start/stop), kds.py router, models (kds/settings/resos — read from
kitchen_db), signalr_listener.py (backoff pre-existing), kds_graphql.py,
database.py. Requirements stripped to ~9 packages; image ~400 MB lighter
than kitchen (no MSSQL ODBC layer).

Frontend: AuthGate (app=kds), single fullscreen route, dark board theme.
KDS.tsx URL prefix patched (/api/kds/ → /kds/api/kds/),
recipe images cross-app (/kitchen/api/recipes/).
nginx: 5 blocks with SSE proxy headers on /kds/api/ block.

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

backend/models/user.py

@@ -0,0 +1,14 @@
+"""
+Type stub — kds.py has `from models.user import User` for the type annotation on
+Depends(get_current_user). At runtime the dependency returns a SimpleNamespace from
+auth.py; this class satisfies the import without pulling in the full SQLAlchemy model.
+"""
+
+
+class User:
+    id: int
+    email: str
+    name: str
+    is_admin: bool
+    kitchen_id: int
+    caps: list