feat(backend): add explicit root /health endpoint for Cloud Run checkups

backend/src/index.ts

@@ -20,6 +20,11 @@ app.disable('x-powered-by');
 app.use(cors({ origin: config.corsOrigin === '*' ? true : config.corsOrigin }));
 app.use(express.json({ limit: '1mb' }));
 
+// Root health check for Cloud Run deployment checks
+app.get('/health', (req, res) => {
+  res.status(200).json({ status: 'ok' });
+});
+
 const apiRoot = config.apiPrefix || '/';
 app.use(apiRoot, createHealthRouter(config));
 app.use(apiRoot, createTodosRouter(config, db));