Seed kitchens id=1 on startup to satisfy kitchen_settings FK

kitchen_settings has a FK to kitchens.id — on a fresh kitchen_db the
kitchens table is empty, so any restore attempt fails with a FK violation.
Idempotent INSERT ON CONFLICT DO NOTHING runs after create_all on every boot.

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

backend/main.py

@@ -3,6 +3,7 @@ from contextlib import asynccontextmanager
 
 from fastapi import FastAPI
 
+from sqlalchemy import text
 from database import engine, Base
 
 logging.basicConfig(
@@ -88,6 +89,9 @@ async def _run(name, coro):
 async def lifespan(app: FastAPI):
     async with engine.begin() as conn:
         await conn.run_sync(Base.metadata.create_all)
+        await conn.execute(
+            text("INSERT INTO kitchens (id, name, created_at) VALUES (1, 'Hotel Number Four', NOW()) ON CONFLICT DO NOTHING")
+        )
 
     await _run("Invoice features", run_migration)
     await _run("Newbook tables", run_newbook_migration)