update /theme to new slash command arch (#3791)

Co-authored-by: matt korwel <matt.korwel@gmail.com>
Co-authored-by: Abhi <43648792+abhipatel12@users.noreply.github.com>

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

@@ -0,0 +1,38 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import { describe, it, expect, beforeEach } from 'vitest';
+import { themeCommand } from './themeCommand.js';
+import { type CommandContext } from './types.js';
+import { createMockCommandContext } from '../../test-utils/mockCommandContext.js';
+
+describe('themeCommand', () => {
+  let mockContext: CommandContext;
+
+  beforeEach(() => {
+    mockContext = createMockCommandContext();
+  });
+
+  it('should return a dialog action to open the theme dialog', () => {
+    // Ensure the command has an action to test.
+    if (!themeCommand.action) {
+      throw new Error('The theme command must have an action.');
+    }
+
+    const result = themeCommand.action(mockContext, '');
+
+    // Assert that the action returns the correct object to trigger the theme dialog.
+    expect(result).toEqual({
+      type: 'dialog',
+      dialog: 'theme',
+    });
+  });
+
+  it('should have the correct name and description', () => {
+    expect(themeCommand.name).toBe('theme');
+    expect(themeCommand.description).toBe('change the theme');
+  });
+});

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

@@ -0,0 +1,16 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import { OpenDialogActionReturn, SlashCommand } from './types.js';
+
+export const themeCommand: SlashCommand = {
+  name: 'theme',
+  description: 'change the theme',
+  action: (_context, _args): OpenDialogActionReturn => ({
+    type: 'dialog',
+    dialog: 'theme',
+  }),
+};

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

@@ -66,7 +66,7 @@ export interface MessageActionReturn {
 export interface OpenDialogActionReturn {
   type: 'dialog';
   // TODO: Add 'theme' | 'auth' | 'editor' | 'privacy' as migration happens.
-  dialog: 'help';
+  dialog: 'help' | 'theme';
 }
 
 export type SlashCommandActionReturn =