feat(doctor): add rig identity beads check

Adds RigBeadsCheck to gt doctor to verify rig identity beads exist.
These beads track rig metadata (git URL, prefix, state) and are created
by gt rig add. The check scans routes.jsonl and verifies each rig
has an identity bead, with --fix to create missing ones.

Recovered from furiosa's uncommitted work after worker interruption.

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

internal/cmd/doctor.go

@@ -135,6 +135,7 @@ func runDoctor(cmd *cobra.Command, args []string) error {
 	d.Register(doctor.NewPatrolPluginsAccessibleCheck())
 	d.Register(doctor.NewPatrolRolesHavePromptsCheck())
 	d.Register(doctor.NewAgentBeadsCheck())
+	d.Register(doctor.NewRigBeadsCheck())
 
 	// NOTE: StaleAttachmentsCheck removed - staleness detection belongs in Deacon molecule