Add critical checks to prevent lost work when polecats call gt done
without having made any commits:
1. Block if working directory not available (cannot verify git state)
2. Block if uncommitted changes exist (would be lost on completion)
3. Check commits against origin/main not local main (ensures actual work)
If any check fails, refuse completion and suggest using --status DEFERRED.
This preserves the worktree so work is not lost.
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
e7b0af0295