fix: update Odoo client for v19 compatibility

- Use persistent httpx client to maintain session cookies
- Update endpoint path to /web/dataset/call_kw/{model}/{method}
- Handle auth response as dict (uid extraction)
- Remove kanban_state field (doesn't exist in Odoo 19)
- Add close() method for graceful shutdown

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

backend/main.py

@@ -73,6 +73,7 @@ async def lifespan(app: FastAPI):
     task = asyncio.create_task(refresh_loop())
     yield
     task.cancel()
+    await odoo_client.close()
 
 
 app = FastAPI(title="TV Dashboard API", lifespan=lifespan)