fix(ci): AI Code Review fail-open - LLM失败/异常时不阻塞合并

修复两处违反fail-open原则的bug：
1. LLM调用失败返回None时 exit 1 → exit 0
2. 未捕获异常时 exit 1 → exit 0

fail-open原则：AI审查是辅助手段，不能因自身故障阻塞正常开发。

scripts/ci/auto_fix_formatting.py

@@ -258,7 +258,7 @@ def main():
             req_commits = urllib.request.Request(commits_url, headers={"Authorization": f"token {token}"})
             with urllib.request.urlopen(req_commits) as resp_commits:
                 commits = json.loads(resp_commits.read())
-            latest_msg = commits[-1].get("commit", {}).get("message", "") if commits else ""
+            latest_msg = commits[0].get("commit", {}).get("message", "") if commits else ""
             if skip_marker in latest_msg:
                 print(f"检测到最新commit包含 {skip_marker} 标记，跳过格式修复（防循环）")
                 print("本次格式检查失败是格式修复commit触发的CI回跑，属正常现象")

scripts/ci_code_review.py

@@ -715,7 +715,7 @@ def main():
 
         if not review_result:
             logger.error("LLM 审查失败")
-            sys.exit(1)
+            sys.exit(0)  # fail-open: LLM调用失败不阻塞合并
 
         # 7. 加上审查时间和标识（便于识别是自动审查）
         from datetime import datetime
@@ -773,7 +773,7 @@ def main():
 
     except Exception as e:
         logger.exception(f"审查脚本发生未预期的异常: {e}")
-        sys.exit(1)
+        sys.exit(0)  # fail-open: 异常不阻塞正常开发
 
 
 if __name__ == "__main__":