Refactor frontend date formatting helpers and mark Task 10 done

frontend/src/components/BanTable.tsx

@@ -27,6 +27,7 @@ import {
 import { PageEmpty, PageError, PageLoading } from "./PageFeedback";
 import { ChevronLeftRegular, ChevronRightRegular } from "@fluentui/react-icons";
 import { useBans } from "../hooks/useBans";
+import { formatTimestamp } from "../utils/formatDate";
 import type { DashboardBanItem, TimeRange, BanOriginFilter } from "../types/ban";
 
 // ---------------------------------------------------------------------------
@@ -90,31 +91,6 @@ const useStyles = makeStyles({
   },
 });
 
-// ---------------------------------------------------------------------------
-// Helpers
-// ---------------------------------------------------------------------------
-
-/**
- * Format an ISO 8601 timestamp for display.
- *
- * @param iso - ISO 8601 UTC string.
- * @returns Localised date+time string.
- */
-function formatTimestamp(iso: string): string {
-  try {
-    return new Date(iso).toLocaleString(undefined, {
-      year: "numeric",
-      month: "2-digit",
-      day: "2-digit",
-      hour: "2-digit",
-      minute: "2-digit",
-      second: "2-digit",
-    });
-  } catch {
-    return iso;
-  }
-}
-
 // ---------------------------------------------------------------------------
 // Column definitions
 // ---------------------------------------------------------------------------