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/database.py

@@ -0,0 +1,38 @@
+import os
+from sqlalchemy.ext.asyncio import create_async_engine, AsyncSession, async_sessionmaker
+from sqlalchemy.orm import DeclarativeBase
+
+DATABASE_URL = os.getenv(
+    "DATABASE_URL",
+    "postgresql+asyncpg://kitchen:kitchen_secret@localhost:5432/kitchen_gp"
+)
+
+# Convert standard postgres URL to asyncpg format
+if DATABASE_URL.startswith("postgresql://"):
+    DATABASE_URL = DATABASE_URL.replace("postgresql://", "postgresql+asyncpg://", 1)
+
+engine = create_async_engine(
+    DATABASE_URL,
+    echo=False,
+    pool_size=10,      # Default is 5
+    max_overflow=20,   # Default is 10 - allows burst to 30 connections
+    pool_pre_ping=True # Verify connections are alive before use
+)
+
+AsyncSessionLocal = async_sessionmaker(
+    engine,
+    class_=AsyncSession,
+    expire_on_commit=False
+)
+
+
+class Base(DeclarativeBase):
+    pass
+
+
+async def get_db():
+    async with AsyncSessionLocal() as session:
+        try:
+            yield session
+        finally:
+            await session.close()