init：代码初始化

src/app.js

@@ -0,0 +1,46 @@
+const express = require('express');
+const cors = require('cors');
+const swaggerUi = require('swagger-ui-express');
+const logger = require('./config/logger');
+const swaggerSpec = require('./config/swagger');
+const routes = require('./routes');
+const { notFound, errorHandler } = require('./middlewares/errorHandler');
+
+/**
+ * 创建 Express 应用
+ */
+function createApp() {
+  const app = express();
+
+  // 中间件配置
+  app.use(cors()); // 跨域支持
+  app.use(express.json()); // JSON 解析
+  app.use(express.urlencoded({ extended: true })); // URL 编码解析
+  app.use(logger); // 日志记录
+
+  // API 文档 - Swagger UI
+  app.use('/api-docs', swaggerUi.serve, swaggerUi.setup(swaggerSpec, {
+    explorer: true,
+    customCss: '.swagger-ui .topbar { display: none }',
+    customSiteTitle: 'Steel Prices Service API Documentation',
+    swaggerOptions: {
+      persistAuthorization: true,
+      displayRequestDuration: true,
+      docExpansion: 'list',
+      filter: true,
+      showRequestHeaders: true,
+      tryItOutEnabled: true
+    }
+  }));
+
+  // 路由
+  app.use('/', routes);
+
+  // 错误处理
+  app.use(notFound);
+  app.use(errorHandler);
+
+  return app;
+}
+
+module.exports = createApp;