plugin update and reinstall do not pull fresh code on Windows — restores from local cache instead

## Environment
- OS: Windows
- Copilot CLI version: 1.0.57
- Reproduced with plugin: `https://github.com/upld-internal/burnrate-copilot.git`

## Description

On Windows, Copilot CLI stores installed plugins in two locations:
- `%USERPROFILE%\.copilot\installed-plugins\_direct\\`
- `%LOCALAPPDATA%\copilot\marketplaces\\`

Running `/plugin update `, or uninstalling and reinstalling, does **not** re-clone from GitHub. It restores files from the `%LOCALAPPDATA%\copilot\marketplaces\\` cache. Plugin updates are never applied.

## Steps to reproduce

1. Install a plugin: `/plugin install https://github.com/upld-internal/burnrate-copilot.git`
2. Push a change to the plugin's GitHub repo
3. Run `/plugin update burnrate-copilot` (or uninstall and reinstall)
4. Check file timestamps: `dir "%USERPROFILE%\.copilot\installed-plugins\_direct\https---github-com-upld-internal-burnrate-copilot-git\scripts\"`
5. Files retain the original install timestamp — updated code is never pulled

## Expected behavior

`/plugin update` re-clones or pulls from GitHub and installs the latest code.

## Actual behavior

Both cache directories retain the original install content. Even after manually deleting `installed-plugins\_direct\\` and reinstalling, files are restored from the `marketplaces` cache rather than fetched from GitHub.

## Workaround

Manually delete **both** cache directories before reinstalling:
```
%USERPROFILE%\.copilot\installed-plugins\_direct\
%LOCALAPPDATA%\copilot\marketplaces\
```