fix(flow): 修复分支切换时 lock 文件冲突问题

在 BranchManager 中添加 _cleanup_lock_file 方法，
在 _merge_normal 和 _merge_with_temp_branch 调用 git checkout 前
先清理可能存在的 lock 文件，避免分支切换失败。

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

.gitignore

@@ -2,4 +2,3 @@ anthropic-agent-skills/
 __pycache__/
 .venv/
 test-cache/
-

aide-program/aide/flow/branch.py

@@ -92,9 +92,18 @@ class BranchManager:
         self.aide_dir = root / ".aide"
         self.branches_json = self.aide_dir / "branches.json"
         self.branches_md = self.aide_dir / "branches.md"
+        self.lock_path = self.aide_dir / "flow-status.lock"
         self._data: BranchesData | None = None
         self._current_branch_info: BranchInfo | None = None
 
+    def _cleanup_lock_file(self) -> None:
+        """清理 lock 文件，避免分支切换时的冲突"""
+        try:
+            if self.lock_path.exists():
+                self.lock_path.unlink()
+        except OSError:
+            pass
+
     def load_branches(self) -> BranchesData:
         """加载分支概况"""
         if self._data is not None:
@@ -314,6 +323,9 @@ class BranchManager:
         source_branch = branch_info.source_branch
         start_commit = branch_info.start_commit
 
+        # 切换分支前清理 lock 文件，避免冲突
+        self._cleanup_lock_file()
+
         # 切回源分支
         self.git.checkout(source_branch)
 
@@ -343,6 +355,9 @@ class BranchManager:
         task_branch = branch_info.branch_name
         temp_branch = f"{task_branch}-merge"
 
+        # 切换分支前清理 lock 文件，避免冲突
+        self._cleanup_lock_file()
+
         # 从起始提交检出临时分支
         self.git.checkout_new_branch(temp_branch, start_commit)