feat(M01-B): 建立核心迁移与MySQL连接池

backend/src/config.ts

@@ -11,6 +11,7 @@ const configSchema = z.object({
   QIPAI_MYSQL_DATABASE: z.string().min(1).default('qipai'),
   QIPAI_MYSQL_USER: z.string().min(1).default('qipai_app'),
   QIPAI_MYSQL_PASSWORD: z.string().default(''),
+  QIPAI_MYSQL_CONNECTION_LIMIT: z.coerce.number().int().min(1).max(50).default(10),
   QIPAI_MQTT_URL: z.string().url().default('mqtt://101.42.38.246:1883'),
   QIPAI_MQTT_USERNAME: z.string().default(''),
   QIPAI_MQTT_PASSWORD: z.string().default('')
@@ -32,7 +33,9 @@ export function loadConfig(env: NodeJS.ProcessEnv = process.env) {
       port: parsed.QIPAI_MYSQL_PORT,
       database: parsed.QIPAI_MYSQL_DATABASE,
       user: parsed.QIPAI_MYSQL_USER,
-      passwordConfigured: parsed.QIPAI_MYSQL_PASSWORD.length > 0
+      password: parsed.QIPAI_MYSQL_PASSWORD,
+      passwordConfigured: parsed.QIPAI_MYSQL_PASSWORD.length > 0,
+      connectionLimit: parsed.QIPAI_MYSQL_CONNECTION_LIMIT
     },
     mqtt: {
       url: parsed.QIPAI_MQTT_URL,

backend/src/db/mysql.ts

@@ -0,0 +1,23 @@
+import mysql, { type Pool, type PoolOptions } from 'mysql2/promise';
+import type { AppConfig } from '../config.js';
+
+export type MySqlPool = Pool;
+
+export function createMySqlPool(config: AppConfig): MySqlPool {
+  return mysql.createPool(toPoolOptions(config));
+}
+
+export function toPoolOptions(config: AppConfig): PoolOptions {
+  return {
+    host: config.mysql.host,
+    port: config.mysql.port,
+    database: config.mysql.database,
+    user: config.mysql.user,
+    password: config.mysql.password,
+    waitForConnections: true,
+    connectionLimit: config.mysql.connectionLimit,
+    namedPlaceholders: true,
+    timezone: 'Z',
+    dateStrings: false
+  };
+}