refactor: extract shared utility functions to eliminate duplication

frontend/src/utils/format.ts

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+/**
+ * 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`;
+}

frontend/src/utils/taskUtils.ts

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+/**
+ * Shared task-related utility functions.
+ *
+ * Consolidates helpers that were duplicated across App.tsx, TaskIndicator.tsx,
+ * TaskProgressDrawer.tsx, and useTaskProgress.ts.
+ */
+
+import type { TaskState, TaskResult } from '@/types';
+
+/** Returns true when the status represents a terminal (finished) task state. */
+export function isTerminalStatus(status: string): boolean {
+    return status === 'SUCCESS' || status === 'FAILURE' || status === 'REVOKED';
+}
+
+/** Convert a TaskState into a TaskResult (for the drawer). */
+export function taskStateToResult(ts: TaskState): TaskResult {
+    return {
+        progress: ts.progress ?? 0,
+        processed: ts.processed,
+        total: ts.total,
+        phase: ts.phase,
+        message: ts.message,
+        subqueries_probed: ts.subqueries_probed,
+        subqueries_initial: ts.subqueries_initial,
+        estimated_results: ts.estimated_results,
+        subqueries_total: ts.subqueries_total,
+        subqueries_completed: ts.subqueries_completed,
+        ids_collected: ts.ids_collected,
+        pages_fetched: ts.pages_fetched,
+        fetching_done: ts.fetching_done,
+        details_fetched: ts.details_fetched,
+        images_downloaded: ts.images_downloaded,
+        ocr_completed: ts.ocr_completed,
+        failed: ts.failed,
+        elapsed_seconds: ts.elapsed_seconds,
+        rate_per_second: ts.rate_per_second,
+        eta_seconds: ts.eta_seconds,
+        logs: ts.logs,
+    };
+}