goal evaluator 的 Stop 钩子在评估失败时 fail-open

缺陷：goal evaluator 的 Stop 钩子在评估失败时 fail-open。 现象：/goal clear 删除目标后，每次会话停止仍触发 "Goal evaluator failed: response was not valid JSON. Treat the goal as incomplete and continue working toward it."，无限阻止停止。 根因（引自 app.asar.unpacked/src-tauri/binaries/claude-sidecar-aarch64-apple-darwin）：