feat: add health check module with unit tests

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

@@ -0,0 +1,29 @@
+import { Test, TestingModule } from '@nestjs/testing';
+import { HealthController } from './health.controller';
+
+describe('HealthController', () => {
+  let controller: HealthController;
+
+  beforeEach(async () => {
+    const module: TestingModule = await Test.createTestingModule({
+      controllers: [HealthController],
+    }).compile();
+    controller = module.get<HealthController>(HealthController);
+  });
+
+  it('returns status "ok"', () => {
+    const result = controller.check();
+    expect(result.status).toBe('ok');
+  });
+
+  it('returns an ISO timestamp', () => {
+    const result = controller.check();
+    expect(() => new Date(result.timestamp)).not.toThrow();
+    expect(result.timestamp).toMatch(/^\d{4}-\d{2}-\d{2}T/);
+  });
+
+  it('returns the service name', () => {
+    const result = controller.check();
+    expect(result.service).toBe('tower-api');
+  });
+});