feat(doctor): add patrol pollution detection and fix

Add CheckPatrolPollution to detect stale patrol beads:
- Patrol digests matching 'Digest: mol-*-patrol'
- Session ended beads matching 'Session ended: *'

Includes auto-fix via 'bd doctor --fix' to clean up pollution.

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

cmd/bd/doctor_fix.go

@@ -312,6 +312,8 @@ func applyFixList(path string, fixes []doctorCheck) {
 			continue
 		case "Legacy MQ Files":
 			err = doctor.FixStaleMQFiles(path)
+		case "Patrol Pollution":
+			err = fix.PatrolPollution(path)
 		default:
 			fmt.Printf("  ⚠ No automatic fix available for %s\n", check.Name)
 			fmt.Printf("  Manual fix: %s\n", check.Fix)