Auto-update "Restart failed" every time — cannot self-update, must reinstall manually (macOS arm64)

### Short summary

_No response_

### Affected version or release

~2.94.0 (macOS 15.7.7, Apple Silicon/arm64)

### Installation context

GitHub Copilot desktop app on macOS (personal machine)

### What happened?

The app shows a "Restart to update" prompt. After pressing Restart, it shows "Restart failed" and I must reinstall manually.

### Steps to reproduce

1. Update prompt appears
2. Click Restart
3. "Restart failed" toast appears

### Expected behavior

Restart applies the update and relaunches into the new version.

### Additional context

Reproduces every update. Likely updater cannot replace the app bundle.

使用报告中的三个步骤在 macOS arm64 上重现更新流程，然后调查为什么 Restart 无法应用更新并重新启动应用。通过 Restart 提示完成更新，并且应用无需手动重新安装即可在新版本中打开时，工作即告完成。

由索引模型根据 Issue 内容生成。