refactor: extract shared formatEur and getTradeStatusDisplay utilities

- Create frontend/app/utils/exchange.ts with shared formatting functions
- Update exchange/page.tsx to use shared formatEur
- Update trades/page.tsx to use shared formatEur and getTradeStatusDisplay
- Update admin/trades/page.tsx to use shared formatEur and getTradeStatusDisplay
- SatsDisplay was already extracted (confirmed it's in components/SatsDisplay.tsx)

frontend/app/utils/exchange.ts

@@ -0,0 +1,59 @@
+/**
+ * Exchange-related utility functions for formatting and display.
+ */
+
+/**
+ * Format EUR amount from cents to display string.
+ * e.g., 10000 -> "€100"
+ */
+export function formatEur(cents: number): string {
+  return `€${(cents / 100).toLocaleString("de-DE")}`;
+}
+
+/**
+ * Get status display properties for trade status badges.
+ */
+export function getTradeStatusDisplay(status: string): {
+  text: string;
+  bgColor: string;
+  textColor: string;
+} {
+  switch (status) {
+    case "booked":
+      return {
+        text: "Pending",
+        bgColor: "rgba(99, 102, 241, 0.2)",
+        textColor: "rgba(129, 140, 248, 0.9)",
+      };
+    case "completed":
+      return {
+        text: "Completed",
+        bgColor: "rgba(34, 197, 94, 0.2)",
+        textColor: "rgba(34, 197, 94, 0.9)",
+      };
+    case "cancelled_by_user":
+      return {
+        text: "User Cancelled",
+        bgColor: "rgba(239, 68, 68, 0.2)",
+        textColor: "rgba(239, 68, 68, 0.9)",
+      };
+    case "cancelled_by_admin":
+      return {
+        text: "Admin Cancelled",
+        bgColor: "rgba(239, 68, 68, 0.2)",
+        textColor: "rgba(239, 68, 68, 0.9)",
+      };
+    case "no_show":
+      return {
+        text: "No Show",
+        bgColor: "rgba(251, 146, 60, 0.2)",
+        textColor: "rgba(251, 146, 60, 0.9)",
+      };
+    default:
+      return {
+        text: status,
+        bgColor: "rgba(255, 255, 255, 0.1)",
+        textColor: "rgba(255, 255, 255, 0.6)",
+      };
+  }
+}