Fix entire cli hanging on prepare-commit-msg git hook

[sbalay]

Problem

Reported this in Discord earlier. After setting up the entire cli in my project, I wasnt able to commit anymore. git commit would just hang.

After some quick research, I found that the root cause for the hang was the entire cli hook: entire hooks git prepare-commit-msg, it just hangs.

Proposed solution

Disclaimer: This solution was written by claude code. I think it makes sense, that's why I'm sending this PR but my knowledge around how the entire cli works is limited

• Fix prepare-commit-msg hook hanging on large repos by replacing go-git's worktree.Status() with native git diff --cached --name-only in getStagedFiles()
  • worktree.Status() scans the entire working tree (O(all files)) — computing hashes, reading .gitignore, comparing with the index — all in pure Go. On repos with deep node_modules or many packages (like stilla-server), this takes 20+ seconds or hangs indefinitely
  • git diff --cached --name-only only lists staged files (O(staged files)), completing in under a second

The codebase already uses exec.CommandContext(ctx, "git", ...) extensively, so this fix reuses and existing pattern, it is not creating a new one:

• paths.WorktreeRoot() — git rev-parse --show-toplevel
• HardResetWithProtection() in common.go — git reset --hard
• CheckoutBranch() in git_operations.go — git checkout
• getUntrackedFiles() in common.go — git ls-files --others
• HasUncommittedChanges() in git_operations.go — git status --porcelain

Test plan

• All existing TestPrepareCommitMsg tests pass
• Full test suite passes (go test ./...)
• Manual test: I built the CLI locally and tested it in my project. It no longer hangs and completes in less than a second