feat(api): app NestJS con configuración validada y health check

Nest 12 (ESM, vitest, oxlint). El .env se valida con zod al arrancar;
prefijo global /api, CORS configurable y GET /api/health.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

apps/api/test/health.e2e-spec.ts

@@ -0,0 +1,24 @@
+import { Test } from '@nestjs/testing';
+import type { INestApplication } from '@nestjs/common';
+import request from 'supertest';
+import { AppModule } from '../src/app.module.js';
+
+describe('Health (e2e)', () => {
+  let app: INestApplication;
+
+  beforeAll(async () => {
+    const moduleRef = await Test.createTestingModule({ imports: [AppModule] }).compile();
+    app = moduleRef.createNestApplication();
+    app.setGlobalPrefix('api');
+    await app.init();
+  });
+
+  afterAll(async () => {
+    await app.close();
+  });
+
+  it('GET /api/health responde ok', async () => {
+    const res = await request(app.getHttpServer()).get('/api/health').expect(200);
+    expect(res.body.status).toBe('ok');
+  });
+});