feat: add gt up/down commands and daemon doctor check

New commands:
- `gt up` - Idempotent boot command that brings up all services:
  Daemon, Deacon, Mayor, and Witnesses for all rigs
- `gt down` - Graceful shutdown of all services

Doctor improvements:
- New daemon check verifies daemon is running
- Fixable with `gt doctor --fix` to auto-start daemon

The system can run degraded (any services down) but `gt up` ensures
a fully operational Gas Town with one idempotent command.

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

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

internal/cmd/doctor.go

@@ -53,6 +53,7 @@ func runDoctor(cmd *cobra.Command, args []string) error {
 	d := doctor.NewDoctor()
 
 	// Register built-in checks
+	d.Register(doctor.NewDaemonCheck())
 	d.Register(doctor.NewBeadsDatabaseCheck())
 
 	// Run checks