malkhut: REQUOTE as proper CANCEL_REPLACE primitive + action_menu metadata

REQUOTE is now distinct from QUOTE:
  QUOTE: PLACE new order (no existing to cancel)
  REQUOTE: CANCEL_REPLACE existing + place new (immediate)
  CHASE: PLACE with short TTL (auto-cancel retry)
  CANCEL: Remove existing order

action_menu generates REQUOTE with metadata={'requote': True} for existing orders.
DSL REQUOTE produces CANCEL_REPLACE when existing order, falls back to PLACE.

All 800+ tests pass.

MALKHUT/malkhut/planner/action_menu.py

@@ -98,6 +98,7 @@ def build_our_actions(
                 price_ticks_from_best=offset, qty_fraction=0.25,
                 ttl_ms=params.passive_ttl_ms, cancel_order_id=oo.client_order_id,
                 post_only=intent.prefer_maker, reduce_only=intent.reduce_only,
+                metadata={"requote": True, "requote_offset": offset},
             ))
 
     # Passive quote placements