feat(commands): friendly /hipico empty-arg response with examples

When /hipico is called without a message, reply with a greeting and
usage examples instead of a plain error message.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

pkg/commands/cmd_mode.go

@@ -51,7 +51,7 @@ func hipicoCmnd() Definition {
 				}
 			}
 			if msg == "" {
-				return req.Reply("Usage: /hipico <message>\nExample: /hipico check the log files for errors")
+				return req.Reply("👋 Hi~ What can I help you with?\n\n💡 Examples:\n  /hipico what files are in the working directory?\n  /hipico what time is it now?\n  /hipico what's the progress on the previous task?")
 			}
 			reply, err := rt.RunOneShot(ctx, msg)
 			if err != nil {