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/interfaces/download-client.interface.ts

@@ -11,7 +11,7 @@
 // =========================================================================
 
 /** Supported download client types — single source of truth */
-export const SUPPORTED_CLIENT_TYPES = ['qbittorrent', 'sabnzbd', 'nzbget', 'transmission'] as const;
+export const SUPPORTED_CLIENT_TYPES = ['qbittorrent', 'sabnzbd', 'nzbget', 'transmission', 'rdtclient'] as const;
 
 /** Identifies the specific download client software */
 export type DownloadClientType = (typeof SUPPORTED_CLIENT_TYPES)[number];
@@ -22,6 +22,7 @@ export const CLIENT_DISPLAY_NAMES: Record<DownloadClientType, string> = {
   sabnzbd: 'SABnzbd',
   nzbget: 'NZBGet',
   transmission: 'Transmission',
+  rdtclient: 'RDT-Client',
 };
 
 /** Get display name for a client type, falling back to the raw type */
@@ -38,6 +39,7 @@ export const CLIENT_PROTOCOL_MAP: Record<DownloadClientType, ProtocolType> = {
   sabnzbd: 'usenet',
   nzbget: 'usenet',
   transmission: 'torrent',
+  rdtclient: 'torrent',
 };
 
 /** Unified download status across all clients */