revert(order): 移除订单站内聊天，沟通统一走官方客服

- 删除 pages/order/chat、聊天接口/仓储方法/order_messages 建表与客户端 API

- 买家「联系大神」、大神「联系老板」、大神详情「在线客服」、组局「私聊」统一改为 openSupportSheet（读取后台 customer_service 配置的客服微信/热线）

- 保留派单实时通知与雷达/大厅轮询

- 114 套件/742 用例全绿；聊天接口线上已 404

server/src/db/mysql.ts

@@ -159,21 +159,6 @@ export async function initDatabase(): Promise<void> {
       ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;
     `);
 
-    // 订单维度站内聊天消息（仅交易双方可见，敏感词/联系方式在服务端拦截）
-    await conn.query(`
-      CREATE TABLE IF NOT EXISTS order_messages (
-        id VARCHAR(64) PRIMARY KEY,
-        order_id VARCHAR(64) NOT NULL,
-        sender_id INT NOT NULL,
-        receiver_id INT NOT NULL,
-        content TEXT NOT NULL,
-        created_at DATETIME DEFAULT CURRENT_TIMESTAMP,
-        read_at DATETIME NULL,
-        INDEX idx_order_created (order_id, created_at),
-        INDEX idx_receiver_read (receiver_id, read_at)
-      ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;
-    `);
-
     const extraOrderCols = [
       "ALTER TABLE orders ADD COLUMN buyer_id INT DEFAULT 1001 AFTER id",
       "ALTER TABLE orders ADD COLUMN expert_id INT DEFAULT 101 AFTER buyer_id",