fix(07): WR-03 replace dead try/catch in formatDateTime with isNaN guard

new Date() never throws so the catch was unreachable. Invalid dates rendered
as NaN.NaN.NaN, NaN:NaN Uhr. Use isNaN(d.getTime()) guard to fall back to
the raw string instead.

apps/web/src/app/(portal)/modules/dkv-fleet/components/InvoiceHistoryTable.tsx

@@ -26,17 +26,17 @@ function DownloadIcon() {
 
 /** Formats an ISO date string as "26.06.2026, 14:32 Uhr" */
 function formatDateTime(isoString: string): string {
-  try {
-    const d = new Date(isoString);
-    const day = String(d.getDate()).padStart(2, '0');
-    const month = String(d.getMonth() + 1).padStart(2, '0');
-    const year = d.getFullYear();
-    const hours = String(d.getHours()).padStart(2, '0');
-    const minutes = String(d.getMinutes()).padStart(2, '0');
-    return `${day}.${month}.${year}, ${hours}:${minutes} Uhr`;
-  } catch {
-    return isoString;
-  }
+  const d = new Date(isoString);
+  // new Date() never throws — it returns an Invalid Date object for bad input.
+  // Check explicitly so malformed strings fall back gracefully instead of
+  // rendering as "NaN.NaN.NaN, NaN:NaN Uhr" (WR-03).
+  if (isNaN(d.getTime())) return isoString;
+  const day = String(d.getDate()).padStart(2, '0');
+  const month = String(d.getMonth() + 1).padStart(2, '0');
+  const year = d.getFullYear();
+  const hours = String(d.getHours()).padStart(2, '0');
+  const minutes = String(d.getMinutes()).padStart(2, '0');
+  return `${day}.${month}.${year}, ${hours}:${minutes} Uhr`;
 }
 
 interface InvoiceHistoryTableProps {