refactor: extract shared utility functions to eliminate duplication

frontend/src/utils/format.ts

@@ -0,0 +1,37 @@
+/**
+ * Shared formatting utility functions.
+ *
+ * Consolidates duplicated formatters that were previously defined inline in
+ * PropertyCard, ListingDetail, MobileBottomSheet, and StatsBar.
+ */
+
+/** Format a number as a compact GBP string, e.g. "£1.2k" or "£950". */
+export function formatCurrency(value: number): string {
+    if (value >= 1000) return `£${(value / 1000).toFixed(1)}k`;
+    return `£${Math.round(value)}`;
+}
+
+/** Format a duration in seconds as a human-readable string, e.g. "12m" or "1h30m". */
+export function formatDuration(seconds: number): string {
+    const minutes = Math.round(seconds / 60);
+    if (minutes < 60) return `${minutes}m`;
+    const hours = Math.floor(minutes / 60);
+    const mins = minutes % 60;
+    return mins > 0 ? `${hours}h${mins}m` : `${hours}h`;
+}
+
+/** Format an ISO date string as a localised short date (e.g. "3 Jan 2025"). */
+export function formatDate(value: string): string {
+    const date = new Date(value);
+    if (isNaN(date.getTime())) return value;
+    return date.toLocaleDateString('en-GB', { day: 'numeric', month: 'short', year: 'numeric' });
+}
+
+/**
+ * Compute the price per square metre as a formatted string, e.g. "£4,500/m²".
+ * Returns null when square metres data is unavailable.
+ */
+export function formatPricePerSqm(price: number, sqm: number | null | undefined): string | null {
+    if (sqm == null || sqm <= 0) return null;
+    return `£${Math.round(price / sqm).toLocaleString()}/m²`;
+}