malkhut: P0 guard + P1 BingX protective strings + tests fixed

P0 (safety): adapter.py rejects unmapped types (OCO, TP_SL) via
  is_type_available() guard. Returns None instead of silent LIMIT fallback.

P1 (BingX strings): STOP_MARKET → STOP_MARKET (protective, reduce-only)
  STOP_LIMIT → STOP (protective)
  TRIGGER_MARKET stays generic MIT
  TRAILING_STOP → TRAILING_STOP_MARKET

Tests updated to match corrected mappings.

MALKHUT/malkhut/venue/bingx/adapter.py

@@ -179,10 +179,17 @@ class BingXVenueAdapter:
 
         # Determine order type — use standardized OrderType, map to BingX-native
         from malkhut.training.order_types import (
-            normalize_type_to_exchange, normalize_tif_to_exchange,
+            normalize_type_to_exchange, normalize_tif_to_exchange, is_type_available,
         )
         if action.order_type is not None:
-            order_type = normalize_type_to_exchange(action.order_type, "bingx") or "LIMIT"
+            if not is_type_available(action.order_type, "bingx"):
+                import logging
+                logging.getLogger(__name__).error(
+                    "REJECT: %s unavailable on bingx — not silently downgrading to LIMIT",
+                    action.order_type.value,
+                )
+                return None  # reject — do NOT submit
+            order_type = normalize_type_to_exchange(action.order_type, "bingx")
         elif action.kind.value == "CROSS_SPREAD":
             order_type = "MARKET"
         else: