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.

packages/features/finance/package.json

@@ -33,5 +33,8 @@
     "react": "catalog:",
     "react-hook-form": "catalog:",
     "zod": "catalog:"
+  },
+  "dependencies": {
+    "lucide-react": "catalog:"
   }
-}
+}