fix: convert Windows path to POSIX notation for core.hooksPath

[Copilot]

install.ps1 was writing a Windows-style path (e.g. C:\Users\...\git\hooks) to core.hooksPath. Git for Windows bash resolves hooks via that config and requires POSIX drive notation (/c/Users/.../git/hooks), so hooks silently failed to run.

Changes

• git-hooks/install.ps1: Before setting core.hooksPath, convert any Windows drive-letter path to POSIX notation. Paths already in POSIX format (Linux/macOS) pass through unchanged.

# Before
git config --global core.hooksPath $HooksDir  # → C:\Users\...\git\hooks

# After
if ($HooksDir -match '^([A-Za-z]):[/\\](.*)$') {
    $drive = $Matches[1].ToLower()
    $rest  = $Matches[2] -replace '\\', '/'
    $posixHooksDir = "/$drive/$rest"           # → /c/Users/.../git/hooks
} else {
    $posixHooksDir = $HooksDir -replace '\\', '/'
}
git config --global core.hooksPath $posixHooksDir

• git-hooks/tests/install.Tests.ps1: Add assertion that core.hooksPath is set to POSIX drive notation (/[a-z]/...) and does not contain C:-style prefix on Windows. Test is gated on $IsWindows so it is a no-op on Linux/macOS.

---

💡 You can make Copilot smarter by setting up custom instructions, customizing its development environment and configuring Model Context Protocol (MCP) servers. Learn more Copilot coding agent tips in the docs.