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/[batchId]/page.tsx

@@ -1,13 +1,13 @@
 import Link from 'next/link';
 
-import { ArrowLeft, Download } from 'lucide-react';
+import { ArrowLeft } from 'lucide-react';
 import { getTranslations } from 'next-intl/server';
 
 import { createFinanceApi } from '@kit/finance/api';
+import { SepaBatchActions } from '@kit/finance/components';
 import { formatDate } from '@kit/shared/dates';
 import { getSupabaseServerClient } from '@kit/supabase/server-client';
 import { Badge } from '@kit/ui/badge';
-import { Button } from '@kit/ui/button';
 import { Card, CardContent, CardHeader, CardTitle } from '@kit/ui/card';
 
 import { AccountNotFound } from '~/components/account-not-found';
@@ -124,10 +124,12 @@ export default async function SepaBatchDetailPage({ params }: PageProps) {
             </dl>
 
             <div className="mt-6">
-              <Button disabled variant="outline">
-                <Download className="mr-2 h-4 w-4" />
-                {t('sepa.downloadXml')}
-              </Button>
+              <SepaBatchActions
+                batchId={batchId}
+                accountId={acct.id}
+                batchStatus={status}
+                itemCount={items.length}
+              />
             </div>
           </CardContent>
         </Card>