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/lib/integrations/prowlarr.service.ts

@@ -640,6 +640,18 @@ export class ProwlarrService {
 // Singleton instance
 let prowlarrService: ProwlarrService | null = null;
 
+/**
+ * Invalidate the cached ProwlarrService singleton.
+ * Must be called after updating Prowlarr URL or API key so that
+ * background jobs (search, RSS monitor, etc.) pick up the new credentials.
+ */
+export function invalidateProwlarrService(): void {
+  if (prowlarrService) {
+    logger.info('Prowlarr service singleton invalidated — will reconnect with new credentials on next use');
+  }
+  prowlarrService = null;
+}
+
 export async function getProwlarrService(): Promise<ProwlarrService> {
   if (!prowlarrService) {
     // Get configuration from database