pd-ctl: fix region keyspace command help text

Clarify that table-id is an optional filter on keyspace lookup and align the new test file header year with the current review update.

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>
Signed-off-by: Ryan Leung <rleungx@gmail.com>

Author: rleungx

tools/pd-ctl/pdctl/command/region_command.go

@@ -538,7 +538,7 @@ func NewRegionWithKeyspaceCommand() *cobra.Command {
 	}
 	r.AddCommand(&cobra.Command{
 		Use:   "id <keyspace_id> [table-id <table_id>] [<limit>]",
-		Short: "show region information for the given keyspace id",
+		Short: "show region information for the given keyspace id, optionally filtered by table id",
 		Run:   showRegionWithKeyspaceCommandFunc,
 	})
 	return r

tools/pd-ctl/pdctl/command/region_command_test.go

@@ -1,4 +1,4 @@
-// Copyright 2025 TiKV Project Authors.
+// Copyright 2026 TiKV Project Authors.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.