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/src/app.module.ts

@@ -0,0 +1,9 @@
+import { Module } from '@nestjs/common';
+import { AppConfigModule } from './config/config.module.js';
+import { HealthController } from './health/health.controller.js';
+
+@Module({
+  imports: [AppConfigModule],
+  controllers: [HealthController],
+})
+export class AppModule {}