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/health/health.controller.ts

@@ -0,0 +1,13 @@
+import { Controller, Get } from '@nestjs/common';
+import type { HealthResponse } from '@tessera/shared';
+
+@Controller('health')
+export class HealthController {
+  @Get()
+  check(): HealthResponse {
+    return {
+      status: 'ok',
+      timestamp: new Date().toISOString(),
+    };
+  }
+}

apps/api/src/health/health.module.ts

@@ -0,0 +1,7 @@
+import { Module } from '@nestjs/common';
+import { HealthController } from './health.controller';
+
+@Module({
+  controllers: [HealthController],
+})
+export class HealthModule {}