fix(git-manager): set upstream when pushing new branches

push() was failing for new fix branches because they had no upstream
tracking branch. Now uses set_upstream=True with explicit refspec.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

repair_agent/agent/git_manager.py

@@ -158,17 +158,15 @@ class GitManager:
             return False
     
     def push(self, branch_name: Optional[str] = None) -> bool:
-        """推送到远程"""
+        """推送到远程（自动设置上游跟踪分支）"""
         if not self.repo:
             return False
 
         try:
+            branch = branch_name or self.repo.active_branch.name
             origin = self.repo.remotes.origin
-            if branch_name:
-                origin.push(branch_name)
-            else:
-                origin.push()
-            logger.info("推送成功")
+            origin.push(refspec=f"{branch}:{branch}", set_upstream=True)
+            logger.info(f"推送成功: {branch}")
             return True
         except Exception as e:
             logger.error(f"推送失败: {e}")