Add RDT-Client support and Prowlarr prompt

Introduce RDT-Client integration and related UI/behavior changes.

- Add RDTClientService extending QBittorrentService with RDT-specific behavior (stale-torrent deletion, postProcess cleanup, no-op categories).
- Register 'rdtclient' in supported client types, display names, and protocol mapping; create RDT client factory in DownloadClientManager.
- Add RDT-Client card to DownloadClientManagement UI and placeholder URL in DownloadClientModal.
- Update qbittorrent service: omit per-torrent savepath/sequential options (favor category/automatic management), make several methods protected, and clean up related comments.
- Make organize-files.processor treat rdtclient as a special-case for cleanup (remove local torrent entries after organize).
- Add prowlarr service singleton invalidation and call it when Prowlarr settings are updated so background jobs pick up new credentials.
- Add confirmation flow when changing Prowlarr URL/API key: new useIndexersSettings logic to detect credential changes, prompt ConfirmModal from IndexersTab, and optionally clear configured indexers on confirmed change.

These changes ensure Real-Debrid-backed qBittorrent-compatible clients are supported correctly and that switching Prowlarr credentials is handled safely.

src/app/api/admin/settings/prowlarr/route.ts

@@ -7,6 +7,7 @@ import { NextRequest, NextResponse } from 'next/server';
 import { requireAuth, requireAdmin, AuthenticatedRequest } from '@/lib/middleware/auth';
 import { prisma } from '@/lib/db';
 import { getEncryptionService } from '@/lib/services/encryption.service';
+import { invalidateProwlarrService } from '@/lib/integrations/prowlarr.service';
 import { RMABLogger } from '@/lib/utils/logger';
 
 const logger = RMABLogger.create('API.Admin.Settings.Prowlarr');
@@ -42,6 +43,9 @@ export async function PUT(request: NextRequest) {
           });
         }
 
+        // Invalidate cached singleton so background jobs use new credentials
+        invalidateProwlarrService();
+
         logger.info('Prowlarr settings updated');
 
         return NextResponse.json({