feat(doctor): Add orphan session and process detection

Add two new health checks to gt doctor:

1. orphan-sessions: Detects Gas Town tmux sessions (gt-*) that do not
   match expected patterns (mayor, deacon, rig-witness, rig-refinery,
   rig-polecat). Validates rig names against actual workspace structure.

2. orphan-processes: Detects Claude/claude-code processes without a
   tmux parent. Walks process tree to find orphaned instances that
   may be consuming resources.

Both checks support --fix to clean up detected orphans:
- Kills orphaned tmux sessions
- Sends SIGINT (then SIGKILL) to orphaned processes

Closes gt-qsvq.

Generated with Claude Code

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

internal/cmd/doctor.go

@@ -55,6 +55,8 @@ func runDoctor(cmd *cobra.Command, args []string) error {
 	// Register built-in checks
 	d.Register(doctor.NewDaemonCheck())
 	d.Register(doctor.NewBeadsDatabaseCheck())
+	d.Register(doctor.NewOrphanSessionCheck())
+	d.Register(doctor.NewOrphanProcessCheck())
 
 	// Run checks
 	var report *doctor.Report