feat: add multi-bill-edit page for batch bill status updates

- Add getLocationsByMonth server action with aggregation pipeline to calculate hasAttachment
- Add updateMonth server action for bulk bill status updates with path revalidation
- Create multi-bill-edit page at /home/multi-bill-edit/[year]/[month]
- Implement MultiBillEdit component with toggle functionality for all bills
- Add BillToggleBadge component integration for consistent bill display
- Add "set all as paid/unpaid" toggle button for batch operations
- Implement server-side redirect with success message after save
- Add Suspense boundary with loading skeleton
- Update translations for multi-bill-edit feature (Croatian and English)
- Ensure data freshness with unstable_noStore and revalidatePath

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

app/[locale]/home/multi-bill-edit/[year]/[month]/not-found.tsx

@@ -0,0 +1,6 @@
+import { NotFoundPage } from '@/app/ui/NotFoundPage';
+ 
+const MultiBillEditNotFound = () =>
+<NotFoundPage title="404 Month Not Found" description="Could not find the requested month." />;
+
+export default MultiBillEditNotFound;