When polecats are nuked, Claude child processes could survive and become
orphans, leading to memory exhaustion (observed: 142 orphaned processes
consuming ~56GB RAM).
This commit:
1. Increases the SIGTERM→SIGKILL grace period from 100ms to 2s to give
processes time to clean up gracefully
2. Adds orphan cleanup to `gt polecat nuke` that runs after session
termination to catch any processes that escaped
3. Adds a new `gt cleanup` command for manual orphan removal
The orphan detection uses aggressive tmux session verification to find
ALL Claude processes not in any active session, not just those with
PPID=1.
Fixes: gh-736
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
bebf425ac5