fix(ai): enforce the tool round limit

Stop after one final-answer turn and pin Pi 0.84.2 for the public stop hook.
到达工具轮次上限后只允许一轮终答，并锁定提供公开停止钩子的 Pi 0.84.2。

apps/cli/package.json

@@ -48,8 +48,8 @@
   "dependencies": {
     "@fastify/multipart": "^10.0.0",
     "@fastify/static": "^9.1.3",
-    "@earendil-works/pi-agent-core": "0.83.0",
-    "@earendil-works/pi-ai": "0.83.0",
+    "@earendil-works/pi-agent-core": "0.84.2",
+    "@earendil-works/pi-ai": "0.84.2",
     "@modelcontextprotocol/sdk": "^1.12.1",
     "better-sqlite3": "^12.4.6",
     "commander": "^13.1.0",