refactor(polecat): remove unused 'cat' alias

The 'cat' alias for 'gt polecat' was never used by agents.
Removing it frees up 'cat' for a more intuitive use case:
displaying bead content (gt cat <bead-id>).

See: bd-dcahx

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

internal/cmd/polecat.go

@@ -30,7 +30,7 @@ var (
 
 var polecatCmd = &cobra.Command{
 	Use:     "polecat",
-	Aliases: []string{"cat", "polecats"},
+	Aliases: []string{"polecats"},
 	GroupID: GroupAgents,
 	Short:   "Manage polecats in rigs",
 	RunE:    requireSubcommand,