Show expiry settlement as index vs strike intrinsic.

Persist settle_index_px and surface formula in trade detail so expiry closes are not mistaken for book fills.

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

frontend/src/labels.ts

@@ -52,10 +52,18 @@ export function positionSidesZh(
   return `${sideZh(perp)}/${sideZh(option)}`;
 }
 
-export function fillDescZh(leg: string, action: string, side: string): string {
+export function fillDescZh(
+  leg: string,
+  action: string,
+  side: string,
+  closeReason?: string | null,
+): string {
   const l = LEG_ZH[leg] || leg;
   const a = ACTION_ZH[action] || action;
   const s = SIDE_ZH[side] || side;
+  if (leg === "option" && action === "close" && closeReason === "expiry") {
+    return "期权到期结算";
+  }
   // 期权买入开仓：「期权开多」；永续：「永续开多/开空」
   if (leg === "option" && action === "open") return "期权开多";
   if (leg === "option" && action === "close") return "期权平多";