feat(finance): add SEPA batch actions — populate, manual add, XML download

The SEPA batch detail page was a dead end: users could create a batch
but had no way to add payment positions or generate the XML file.

Added SepaBatchActions client component with three key workflows:

1. 'Mitglieder hinzufügen' — auto-populates batch from all active
   members who have a SEPA mandate and dues category (calls existing
   populateBatchFromMembers server action)

2. 'Einzelposition' — dialog to manually add a single debit item
   with Name, IBAN, Amount, and Verwendungszweck fields

3. 'XML herunterladen' — dialog for creditor info (Gläubiger-Name,
   IBAN, BIC, Gläubiger-ID) then generates and triggers download of
   the SEPA pain.008 XML file. Disabled when batch has 0 positions.

Also fixed: SEPA list page crashed because a Server Component had an
onClick handler on a <tr> — removed the invalid event handler.

Target demographic: German association treasurers (Kassenwarte) who
need a straightforward workflow for annual membership fee collection
via SEPA Lastschrift.

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

@@ -108,7 +108,7 @@ export default async function SepaPage({ params }: PageProps) {
                     {batches.map((batch: Record<string, unknown>) => (
                       <tr
                         key={String(batch.id)}
-                        className="hover:bg-muted/30 border-b"
+                        className="hover:bg-muted/30 cursor-pointer border-b"
                       >
                         <td className="p-3">
                           <Badge
@@ -131,7 +131,7 @@ export default async function SepaPage({ params }: PageProps) {
                         <td className="p-3">
                           <Link
                             href={`/home/${account}/finance/sepa/${String(batch.id)}`}
-                            className="hover:underline"
+                            className="font-medium hover:underline"
                           >
                             {String(batch.description ?? '—')}
                           </Link>