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/mail.go

@@ -41,8 +41,9 @@ var (
 )
 
 var mailCmd = &cobra.Command{
-	Use:   "mail",
-	Short: "Agent messaging system",
+	Use:     "mail",
+	GroupID: GroupComm,
+	Short:   "Agent messaging system",
 	Long: `Send and receive messages between agents.
 
 The mail system allows Mayor, polecats, and the Refinery to communicate.