Unable to add-dir with user home directory (Windows)

### Describe the bug

When using /add-dir command, if trying to use ~ for home directory, backslash fails to recognize. It's necessary to use forward-slash, but the autocomplete keeps replacing my forward-slash with backslash.

### Affected version

GitHub Copilot CLI 1.0.60

### Steps to reproduce the behavior

/add-dir ~/.agents/skills
Autocomplete will turn it into ~\.agents\skills and I can't override it
add-dir command fails

### Expected behavior

Expect /add-dir with ~\ to work correctly OR
Autocomplete doesn't replace / with \

### Additional context

Windows 11
Using Windows Terminal with pwsh 7

Start by reproducing `/add-dir ~/.agents/skills` on Windows 11 with PowerShell 7 and observe the autocomplete transformation. Inspect the `/add-dir` command and its autocomplete path handling; done means a home-directory path with `~` works, or the autocomplete no longer forces backslashes in a way that makes the command fail.

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