feat: switch to Docker Compose + auto-migration

- docker-compose.yml: 移除 MySQL 容器，后端连宿主机 MySQL
- main.ts: 启动时自动 runMigrations
- 前端 Nginx 反代 /api/ → backend:3000 不变

apps/server/src/main.ts

@@ -1,12 +1,15 @@
 import { NestFactory } from '@nestjs/core';
 import { ValidationPipe } from '@nestjs/common';
 import { AppModule } from './app.module';
+import { DataSource } from 'typeorm';
 
 async function bootstrap() {
   const app = await NestFactory.create(AppModule);
   app.setGlobalPrefix('api');
   app.enableCors();
-  app.useGlobalPipes(new ValidationPipe({ transform: true, whitelist: true }));
+  const dataSource = app.get(DataSource);
+  await dataSource.runMigrations();
+  console.log('Migrations OK');
   await app.listen(process.env.PORT ?? 3000);
   console.log(`Server running on http://localhost:${process.env.PORT ?? 3000}`);
 }