fix(feishu): fix webhook mode silent exit and receive_id_type default

- monitor.ts: throw error for webhook mode instead of silently returning,
  so gateway properly marks channel as failed
- targets.ts: default receive_id_type to "user_id" instead of "open_id"
  for non-prefixed IDs, fixing message delivery for enterprise user IDs

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

extensions/feishu/src/monitor.ts

@@ -55,7 +55,9 @@ export async function monitorFeishuProvider(opts: MonitorFeishuOpts = {}): Promi
     });
   }
 
-  log("feishu: webhook mode not implemented in monitor, use HTTP server directly");
+  throw new Error(
+    "feishu: webhook mode not implemented in monitor. Use websocket mode or configure an external HTTP server.",
+  );
 }
 
 async function monitorWebSocket(params: {