Add Binance SIM market adapter and exchange switch in settings.

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

backend/app/exchange/factory.py

@@ -2,20 +2,22 @@
 
 from __future__ import annotations
 
-from ..config import Settings, get_settings
+from ..config import 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()
+    from .runtime import load_runtime_settings, normalize_exchange_name
+
+    s = settings or load_runtime_settings()
+    name = normalize_exchange_name(s.exchange)
     if name == "okx":
         from .okx.adapter import OkxExchange
 
         return OkxExchange(s)
-    if name in ("binance", "bn"):
+    if name == "binance":
         from .binance.adapter import BinanceExchange
 
         return BinanceExchange(s)