feat(ui): add /settings command and UI panel (#4738)

Co-authored-by: Jacob Richman <jacob314@gmail.com>

packages/cli/src/ui/commands/settingsCommand.test.ts

@@ -0,0 +1,36 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import { describe, it, expect, beforeEach } from 'vitest';
+import { settingsCommand } from './settingsCommand.js';
+import { type CommandContext } from './types.js';
+import { createMockCommandContext } from '../../test-utils/mockCommandContext.js';
+
+describe('settingsCommand', () => {
+  let mockContext: CommandContext;
+
+  beforeEach(() => {
+    mockContext = createMockCommandContext();
+  });
+
+  it('should return a dialog action to open the settings dialog', () => {
+    if (!settingsCommand.action) {
+      throw new Error('The settings command must have an action.');
+    }
+    const result = settingsCommand.action(mockContext, '');
+    expect(result).toEqual({
+      type: 'dialog',
+      dialog: 'settings',
+    });
+  });
+
+  it('should have the correct name and description', () => {
+    expect(settingsCommand.name).toBe('settings');
+    expect(settingsCommand.description).toBe(
+      'View and edit Gemini CLI settings',
+    );
+  });
+});