feat(core): agnostic background task UI with CompletionBehavior (#22740)

Co-authored-by: mkorwel <matt.korwel@gmail.com>

packages/cli/src/ui/commands/tasksCommand.ts

@@ -0,0 +1,18 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import { CommandKind, type SlashCommand } from './types.js';
+
+export const tasksCommand: SlashCommand = {
+  name: 'tasks',
+  altNames: ['bg', 'background'],
+  kind: CommandKind.BUILT_IN,
+  description: 'Toggle background tasks view',
+  autoExecute: true,
+  action: async (context) => {
+    context.ui.toggleBackgroundTasks();
+  },
+};