feat(01-01): NestJS API with health endpoint and Prisma schema

- NestJS app with ConfigModule and HealthModule
- GET /health endpoint returning {status, timestamp} using HealthResponse type
- Prisma schema with PostgreSQL datasource and Tenant model (multi-tenancy foundation)
- Multi-stage Dockerfile with non-root nestjs user, monorepo root as build context
- Workspace dependency on @tessera/shared for shared types
- Type-check passes successfully

apps/api/src/main.ts

@@ -0,0 +1,13 @@
+import { NestFactory } from '@nestjs/core';
+import { AppModule } from './app.module';
+
+async function bootstrap() {
+  const app = await NestFactory.create(AppModule);
+
+  app.enableCors({ origin: true });
+
+  await app.listen(3001);
+  console.log('Tessera API running on port 3001');
+}
+
+bootstrap();