Question about "Direct plugin installs (repos, URLs, local paths) are deprecated. "

Recently (as of version 1.0.35-0 or so), I started getting this warning when running `copilot plugin install /path/to/plugin/on/my/machine`:

```
⚠️ Warning: Direct plugin installs (repos, URLs, local paths) are deprecated. Only plugin@marketplace installs will be supported in a future release.
```

Can anyone shed some light on why this change is being made? Also, will this affect the `--plugin-dir` CLI option too, meaning all custom plugins will have to come from marketplace, or will there always be some local source for custom agents, hooks, etc?

從報告中提到的 `copilot plugin install /path/to/plugin/on/my/machine` 命令和 `--plugin-dir` CLI 選項開始。檢查外掛程式安裝和 CLI 的文件或行為，以確定本機來源是否仍受支援，並記錄棄用的理由和未來範圍。兩項問題都有權威答案時即完成。

由索引模型根據 Issue 內容生成。