feat: 接入 USDT-M 合约数据 — type 字段方案

- PairType 定义移至 types/kline.ts (spot/um/cm)
- Kline 接口新增 type 字段，全链路透传
- klines 5列复合主键 (exchange, symbol, type, interval, time)
- 拆出 BinanceFuturesRestClient (USDMClient)
- exchanges/index.ts 注册 binance_futures
- trading_pairs 唯一约束加 type，种子数据加合约对
- 12个连续聚合视图 SELECT/GROUP BY/INDEX 加 type
- 清理 bnkline.ts 废弃代码和 pair.ts 空函数

data/exchanges/index.ts

@@ -1,9 +1,10 @@
 import { BaseRestClient } from "./base";
-import { BinanceRestClient } from "./binance/rest";
+import { BinanceRestClient, BinanceFuturesRestClient } from "./binance/rest";
 
 /** 交易所 ID 到 RestClient 构造器的注册表 */
 const registry: Record<string, () => BaseRestClient> = {
     binance: () => new BinanceRestClient(),
+    binance_futures: () => new BinanceFuturesRestClient(),
 };
 
 /**
@@ -28,5 +29,5 @@ export function createRestClient(exchangeId: string): BaseRestClient {
 }
 
 export { BaseRestClient } from "./base";
-export { BinanceRestClient } from "./binance/rest";
+export { BinanceRestClient, BinanceFuturesRestClient } from "./binance/rest";
 export { KLINE_INTERVAL_MS } from "./constants";