Split exchange and strategy modules for future Binance support.

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/app/exchange/factory.py

@@ -0,0 +1,34 @@
+"""按配置创建交易所实例。"""
+
+from __future__ import annotations
+
+from ..config import Settings, get_settings
+from .protocol import ExchangeMarket
+
+_exchange: ExchangeMarket | None = None
+
+
+def build_exchange(settings: Settings | None = None) -> ExchangeMarket:
+    s = settings or get_settings()
+    name = (s.exchange or "okx").strip().lower()
+    if name == "okx":
+        from .okx.adapter import OkxExchange
+
+        return OkxExchange(s)
+    if name in ("binance", "bn"):
+        from .binance.adapter import BinanceExchange
+
+        return BinanceExchange(s)
+    raise ValueError(f"未知交易所 EXCHANGE={s.exchange!r}，支持 okx / binance")
+
+
+def get_exchange() -> ExchangeMarket:
+    global _exchange
+    if _exchange is None:
+        _exchange = build_exchange()
+    return _exchange
+
+
+def set_exchange(ex: ExchangeMarket | None) -> None:
+    global _exchange
+    _exchange = ex