Add default USD-M perpetual BTC/ETH/BNB and fix futures WS stream

Seed um BTCUSDT/ETHUSDT/BNBUSDT as default symbols. The legacy futures
route fstream.binance.com/stream accepts connections but no longer pushes
data, so switch to /market/stream. Receive with a timeout so symbol
changes are picked up and silent connections are reconnected.

backend/src/alphapulse/market/binance.py

@@ -15,7 +15,8 @@ REST = {
     "um": {"base": "https://fapi.binance.com", "klines": "/fapi/v1/klines", "exchange_info": "/fapi/v1/exchangeInfo",
            "ticker": "/fapi/v1/ticker/24hr", "weight_limit": 2400, "kline_limit": 1500},
 }
-WS = {"spot": "wss://stream.binance.com:9443/stream", "um": "wss://fstream.binance.com/stream"}
+# 合约旧路由 fstream.binance.com/stream 能连上但不推送数据，K 线/行情流在 /market 路由下
+WS = {"spot": "wss://stream.binance.com:9443/stream", "um": "wss://fstream.binance.com/market/stream"}
 
 # 权重用量超过上限的这个比例就等到下一分钟
 WEIGHT_RATIO = 0.5

backend/src/alphapulse/market/worker.py

@@ -26,6 +26,8 @@ logger = logging.getLogger("alphapulse.market.worker")
 PAGES_PER_TURN = 20
 CATCHUP_SECONDS = 3600
 SYMBOL_CHECK_SECONDS = 10
+# miniTicker 约每秒推送，这么久没消息视为连接卡死
+STALL_SECONDS = 60
 ACTIVE_STATUSES = ("pending", "backfilling", "ready")
 
 client = BinanceClient()
@@ -209,8 +211,19 @@ async def stream_loop(market: str) -> None:
                 logger.info("%s WS 已连接：%d 个交易对，%d 个流", market, len(symbols), len(streams))
                 catchup_needed.set()
                 next_check = time.monotonic() + SYMBOL_CHECK_SECONDS
-                async for raw in ws:
-                    await handle_message(market, raw)
+                last_message = time.monotonic()
+                while True:
+                    # 带超时接收：没有消息时也要按时检查交易对变化和连接是否卡死
+                    try:
+                        raw = await asyncio.wait_for(ws.recv(), timeout=SYMBOL_CHECK_SECONDS)
+                    except TimeoutError:
+                        pass
+                    else:
+                        last_message = time.monotonic()
+                        await handle_message(market, raw)
+                    if time.monotonic() - last_message >= STALL_SECONDS:
+                        logger.warning("%s WS %ds 未收到消息，重连", market, STALL_SECONDS)
+                        break
                     if time.monotonic() >= next_check:
                         next_check = time.monotonic() + SYMBOL_CHECK_SECONDS
                         if await active_symbols(market) != symbols: