Add W017 warning to cmdValidateHealth that detects linked git worktrees that are stale (older than 1 hour, likely from crashed agents) or orphaned (path no longer exists on disk). Parses git worktree list --porcelain output, skips the main worktree, and provides actionable fix suggestions. Gracefully degrades if git worktree is unavailable.
Closes#2167
Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
