fix(git): remove worktrees with missing gitfile

[markwylde]

Summary

• recover forced worktree deletion when the worktree's .git file is already missing or invalid
• remove the orphaned directory before pruning Git's stale worktree registration
• preserve non-forced deletion safety and existing handling for already-missing worktrees
• add regression coverage for the exact broken-gitfile scenario, including untracked content

Testing

• npm run test:git-worktree-status
• npm run lint
• npm run build:app