feat: add command aliases for PGT parity (may, sess, ref, sp, cat, stat)

Add Cobra aliases to match PGT abbreviation support:
- mayor → may (gt may at now works)
- session → sess
- refinery → ref
- spawn → sp
- polecat → cat
- status → stat

This enables the same abbreviated commands that worked in PGT, like
"gt may at" to attach to the Mayor session.

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

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

internal/cmd/spawn.go

@@ -29,8 +29,9 @@ var (
 )
 
 var spawnCmd = &cobra.Command{
-	Use:   "spawn <rig/polecat> | <rig>",
-	Short: "Spawn a polecat with work assignment",
+	Use:     "spawn <rig/polecat> | <rig>",
+	Aliases: []string{"sp"},
+	Short:   "Spawn a polecat with work assignment",
 	Long: `Spawn a polecat with a work assignment.
 
 Assigns an issue or task to a polecat and starts a session. If no polecat