feat(doctor): add orphaned-attachments check (gt-h6eq.3)

Add doctor check to detect handoff beads for agents that no longer exist.
This happens when a polecat worktree is deleted but its handoff bead remains.

- Check: orphaned-attachments
- Warning if: Handoff bead exists for agent that no longer has worktree
- Supports polecats (rig/name), crew (rig/crew/name), mayor, witness, refinery
- Suggests re-sling to active agent or close the molecule

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

internal/cmd/doctor.go

@@ -102,6 +102,7 @@ func runDoctor(cmd *cobra.Command, args []string) error {
 	// Hook attachment checks
 	d.Register(doctor.NewHookAttachmentValidCheck())
 	d.Register(doctor.NewHookSingletonCheck())
+	d.Register(doctor.NewOrphanedAttachmentsCheck())
 
 	// Run checks
 	var report *doctor.Report