feat(mq): Add 'mr' alias for merge request operations (gt-t85hw)

Adds 'gt mr' as an alias for 'gt mq' so both work:
- gt mr submit → gt mq submit
- gt mr status → gt mq status
- gt mr list → gt mq list

'MR' (merge request) is the conceptual noun; 'mq' (merge queue) is the
implementation detail. This reduces friction for agents and humans who
think in terms of "I have a merge request."

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

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

internal/cmd/mq.go

@@ -51,10 +51,13 @@ var (
 
 var mqCmd = &cobra.Command{
 	Use:     "mq",
+	Aliases: []string{"mr"},
 	GroupID: GroupWork,
 	Short:   "Merge queue operations",
 	RunE:    requireSubcommand,
-	Long: `Manage the merge queue for a rig.
+	Long: `Manage merge requests and the merge queue for a rig.
+
+Alias: 'gt mr' is equivalent to 'gt mq' (merge request vs merge queue).
 
 The merge queue tracks work branches from polecats waiting to be merged.
 Use these commands to view, submit, retry, and manage merge requests.`,