feat: enhance accessibility and testing with data-test attributes and improve error handling

apps/web/app/[locale]/home/[account]/finance/invoices/[id]/page.tsx

@@ -55,7 +55,7 @@ export default async function InvoiceDetailPage({ params }: PageProps) {
   const api = createFinanceApi(client);
   const invoice = await api.getInvoiceWithItems(id);
 
-  if (!invoice) return <div>Rechnung nicht gefunden</div>;
+  if (!invoice) return <AccountNotFound />;
 
   const status = String(invoice.status);
   const items = (invoice.items ?? []) as Array<Record<string, unknown>>;

apps/web/app/[locale]/home/[account]/finance/sepa/[batchId]/page.tsx

@@ -74,7 +74,7 @@ export default async function SepaBatchDetailPage({ params }: PageProps) {
     api.getBatchItems(batchId),
   ]);
 
-  if (!batch) return <div>Einzug nicht gefunden</div>;
+  if (!batch) return <AccountNotFound />;
 
   const status = String(batch.status);