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?

从报告中提到的 `copilot plugin install /path/to/plugin/on/my/machine` 命令和 `--plugin-dir` CLI 选项开始。检查插件安装和 CLI 的文档或行为，以确定本地源是否仍受支持，并记录弃用的理由和未来范围。两项问题都有权威答案时即完成。

由索引模型根据 Issue 内容生成。