feat: Add gcloud-style command grouping to gt help output

Organize 43 commands into 7 logical groups using cobra's built-in
AddGroup/GroupID feature:

- Work Management: spawn, sling, hook, handoff, done, mol, mq, etc.
- Agent Management: mayor, witness, refinery, deacon, polecat, etc.
- Communication: mail, nudge, broadcast, peek
- Services: daemon, start, stop, up, down, shutdown
- Workspace: rig, crew, init, install, git-init, namepool
- Configuration: account, theme, hooks, issue, completion
- Diagnostics: status, doctor, prime, version, help

Also renamed molecule to mol as the primary command name
(molecule is now an alias).

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

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

internal/cmd/handoff.go

@@ -14,8 +14,9 @@ import (
 )
 
 var handoffCmd = &cobra.Command{
-	Use:   "handoff [bead-or-role]",
-	Short: "Hand off to a fresh session, work continues from hook",
+	Use:     "handoff [bead-or-role]",
+	GroupID: GroupWork,
+	Short:   "Hand off to a fresh session, work continues from hook",
 	Long: `End watch. Hand off to a fresh agent session.
 
 This is the canonical way to end any agent session. It handles all roles: