fix(tui): deferred command output during streaming

- Queued transcript command panels until the active agent turn ends.

- Added regression coverage for slash-command output mounting exactly once.

Fixes #4806

packages/coding-agent/src/modes/controllers/command-controller-shared.ts

@@ -105,5 +105,5 @@ export function showCommandMessage(ctx: InteractiveModeContext, text: string): v
 	block.addChild(new DynamicBorder());
 	block.addChild(new Text(text, 1, 1));
 	block.addChild(new DynamicBorder());
-	ctx.present(block);
+	ctx.presentCommandOutput(block);
 }