feat(center): validate required env on startup

Fabric.Backend.Center/src/main.ts

@@ -2,7 +2,28 @@ import 'reflect-metadata';
 import { NestFactory } from '@nestjs/core';
 import { AppModule } from './app.module';
 
+function requireEnv(name: string): string {
+  const value = process.env[name];
+  if (!value || value.trim() === '') {
+    throw new Error(`Missing required env: ${name}`);
+  }
+  return value;
+}
+
+function validateEnv(): void {
+  requireEnv('DB_HOST');
+  requireEnv('DB_PORT');
+  requireEnv('DB_USER');
+  requireEnv('DB_PASSWORD');
+  requireEnv('DB_NAME');
+  requireEnv('CENTER_SHARED_SECRET');
+  requireEnv('JWT_ACCESS_SECRET');
+  requireEnv('JWT_REFRESH_SECRET');
+}
+
 async function bootstrap() {
+  validateEnv();
+
   const app = await NestFactory.create(AppModule);
   app.setGlobalPrefix('api');
   const port = process.env.PORT ? Number(process.env.PORT) : 7001;