feat(api): add GroupsModule with GET /groups endpoint

Implements TDD-driven GroupsService and GroupsController with full unit test coverage. GET /groups returns all groups ordered by name, selecting id, name, platform, platformId, isActive, and accountId fields.

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

apps/api/src/modules/groups/groups.controller.spec.ts

@@ -0,0 +1,26 @@
+import { Test, TestingModule } from '@nestjs/testing';
+import { GroupsController } from './groups.controller';
+import { GroupsService } from './groups.service';
+
+const mockGroups = [
+  { id: 'grp_1', name: 'Alpha', platform: 'whatsapp', platformId: '111@g.us', isActive: true, accountId: 'acc_1' },
+];
+const mockService = { list: jest.fn().mockResolvedValue(mockGroups) };
+
+describe('GroupsController', () => {
+  let controller: GroupsController;
+
+  beforeEach(async () => {
+    const module: TestingModule = await Test.createTestingModule({
+      controllers: [GroupsController],
+      providers: [{ provide: GroupsService, useValue: mockService }],
+    }).compile();
+    controller = module.get<GroupsController>(GroupsController);
+  });
+
+  it('returns groups from service', async () => {
+    const result = await controller.list();
+    expect(result).toEqual(mockGroups);
+    expect(mockService.list).toHaveBeenCalled();
+  });
+});