重构后端服务架构并优化前端错误处理

fastapi-backend/.env.example

@@ -0,0 +1,15 @@
+# Database configuration
+DB_HOST=localhost
+DB_PORT=3306
+DB_USER=root
+DB_PASSWORD=password
+DB_NAME=niumall_dev
+
+# JWT configuration
+JWT_SECRET=niumall-jwt-secret
+JWT_ALGORITHM=HS256
+JWT_EXPIRATION_MINUTES=1440
+
+# Server configuration
+SERVER_HOST=0.0.0.0
+SERVER_PORT=8000