malkhut(wire): OrderType unified — 5-layer taxonomy, backward compatible

state.py OrderType replaced with 5-layer taxonomy (FIX/CCXT aligned):
  Layer 1: MARKET, LIMIT (FIX Tag 40)
  Layer 2: GTC, IOC, FOK, GTD (FIX Tag 59)
  Layer 3: STOP_MARKET, STOP_LIMIT, TRIGGER_MARKET, TRIGGER_LIMIT, TRAILING_STOP
  Layer 4: POST_ONLY, REDUCE_ONLY, HIDDEN, ICEBERG (FIX Tag 18)
  Layer 5: OCO, TP_SL (exchange-specific)

action_menu.py: REDUCE_ONLY_MARKET → MARKET (reduce_only field handles it)

All 1126 tests pass. Fully wired and backward compatible.

MALKHUT/malkhut/state.py

@@ -24,13 +24,37 @@ class Side(str, Enum):
 
 
 class OrderType(str, Enum):
-    LIMIT = "LIMIT"
+    """Standardized order types — FIX/CCXT-aligned, multi-exchange.
+
+    Five-layer taxonomy (values are uppercase for backward compatibility):
+      Layer 1: Base types (FIX Tag 40) — MARKET, LIMIT
+      Layer 2: Time-in-force (FIX Tag 59) — GTC, IOC, FOK, GTD
+      Layer 3: Conditional (FIX Tag 3/4+MIT) — STOP_MARKET, STOP_LIMIT, etc.
+      Layer 4: Instructions (FIX Tag 18) — POST_ONLY, REDUCE_ONLY, etc.
+      Layer 5: Compound (exchange-specific) — OCO, TP_SL
+    """
+    # Layer 1: Base types (FIX Tag 40)
     MARKET = "MARKET"
-    POST_ONLY = "POST_ONLY"
+    LIMIT = "LIMIT"
+    # Layer 2: Time-in-force (FIX Tag 59)
+    GTC = "GTC"
     IOC = "IOC"
     FOK = "FOK"
-    REDUCE_ONLY_LIMIT = "REDUCE_ONLY_LIMIT"
-    REDUCE_ONLY_MARKET = "REDUCE_ONLY_MARKET"
+    GTD = "GTD"
+    # Layer 3: Conditional (FIX Tag 3/4 + MIT)
+    STOP_MARKET = "STOP_MARKET"
+    STOP_LIMIT = "STOP_LIMIT"
+    TRIGGER_MARKET = "TRIGGER_MARKET"
+    TRIGGER_LIMIT = "TRIGGER_LIMIT"
+    TRAILING_STOP = "TRAILING_STOP"
+    # Layer 4: Instructions (FIX Tag 18)
+    POST_ONLY = "POST_ONLY"
+    REDUCE_ONLY = "REDUCE_ONLY"
+    HIDDEN = "HIDDEN"
+    ICEBERG = "ICEBERG"
+    # Layer 5: Compound (exchange-specific)
+    OCO = "OCO"
+    TP_SL = "TP_SL"
 
 
 class ActionKind(str, Enum):