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/admin/settings/page.tsx

@@ -295,6 +295,7 @@ export default function AdminSettings() {
           {activeTab === 'prowlarr' && (
             <IndexersTab
               settings={settings}
+              originalSettings={originalSettings}
               indexers={configuredIndexers}
               flagConfigs={flagConfigs}
               onChange={setSettings}

src/app/admin/settings/tabs/IndexersTab/IndexersTab.tsx

@@ -7,6 +7,7 @@
 
 import React, { useEffect } from 'react';
 import { Button } from '@/components/ui/Button';
+import { ConfirmModal } from '@/components/ui/ConfirmModal';
 import { Input } from '@/components/ui/Input';
 import { IndexerManagement } from '@/components/admin/indexers/IndexerManagement';
 import { FlagConfigRow } from '@/components/admin/FlagConfigRow';
@@ -16,6 +17,7 @@ import type { Settings, SavedIndexerConfig } from '../../lib/types';
 
 interface IndexersTabProps {
   settings: Settings;
+  originalSettings: Settings | null;
   indexers: SavedIndexerConfig[];
   flagConfigs: IndexerFlagConfig[];
   onChange: (settings: Settings) => void;
@@ -27,6 +29,7 @@ interface IndexersTabProps {
 
 export function IndexersTab({
   settings,
+  originalSettings,
   indexers,
   flagConfigs,
   onChange,
@@ -35,11 +38,23 @@ export function IndexersTab({
   onValidationChange,
   onRefreshIndexers,
 }: IndexersTabProps) {
-  const { testing, testResult, testConnection } = useIndexersSettings({
+  const {
+    testing,
+    testResult,
+    testConnection,
+    showConnectionChangeConfirm,
+    confirmConnectionChange,
+    cancelConnectionChange,
+    configuredIndexersCount,
+  } = useIndexersSettings({
     prowlarrUrl: settings.prowlarr.url,
     prowlarrApiKey: settings.prowlarr.apiKey,
+    originalProwlarrUrl: originalSettings?.prowlarr.url ?? '',
+    originalProwlarrApiKey: originalSettings?.prowlarr.apiKey ?? '',
+    configuredIndexersCount: indexers.length,
     onValidationChange,
     onRefreshIndexers,
+    onClearIndexers: () => onIndexersChange([]),
   });
 
   // Auto-load indexers when component mounts if prowlarr is configured
@@ -96,7 +111,7 @@ export function IndexersTab({
           placeholder="Enter API key"
         />
         <p className="text-sm text-gray-500 dark:text-gray-400 mt-1">
-          Found in Prowlarr Settings → General → Security → API Key
+          Found in Prowlarr Settings &rarr; General &rarr; Security &rarr; API Key
         </p>
       </div>
 
@@ -178,6 +193,19 @@ export function IndexersTab({
           </p>
         )}
       </div>
+
+      {/* Confirmation modal for Prowlarr connection change */}
+      <ConfirmModal
+        isOpen={showConnectionChangeConfirm}
+        onClose={cancelConnectionChange}
+        onConfirm={confirmConnectionChange}
+        title="Prowlarr Connection Change"
+        message={`Changing your Prowlarr connection will remove your ${configuredIndexersCount} configured indexer${configuredIndexersCount === 1 ? '' : 's'}. Indexer IDs are specific to each Prowlarr instance, so existing configurations cannot be preserved. You will need to re-add indexers from the new instance after saving.`}
+        confirmText="Continue"
+        cancelText="Cancel"
+        variant="danger"
+        isLoading={testing}
+      />
     </div>
   );
 }

src/app/admin/settings/tabs/IndexersTab/useIndexersSettings.ts

@@ -5,30 +5,50 @@
 
 'use client';
 
-import { useState } from 'react';
+import { useState, useCallback } from 'react';
 import { fetchWithAuth } from '@/lib/utils/api';
 import type { TestResult } from '../../lib/types';
 
 interface UseIndexersSettingsProps {
   prowlarrUrl: string;
   prowlarrApiKey: string;
+  originalProwlarrUrl: string;
+  originalProwlarrApiKey: string;
+  configuredIndexersCount: number;
   onValidationChange: (isValid: boolean) => void;
   onRefreshIndexers?: () => Promise<void>;
+  onClearIndexers: () => void;
 }
 
 export function useIndexersSettings({
   prowlarrUrl,
   prowlarrApiKey,
+  originalProwlarrUrl,
+  originalProwlarrApiKey,
+  configuredIndexersCount,
   onValidationChange,
   onRefreshIndexers,
+  onClearIndexers,
 }: UseIndexersSettingsProps) {
   const [testing, setTesting] = useState(false);
   const [testResult, setTestResult] = useState<TestResult | null>(null);
+  const [showConnectionChangeConfirm, setShowConnectionChangeConfirm] = useState(false);
 
   /**
-   * Test Prowlarr connection
+   * Detect if the Prowlarr URL or API key has changed from the saved values.
+   * A masked API key (starting with dots) means the user hasn't touched it.
    */
-  const testConnection = async () => {
+  const hasConnectionChanged = useCallback((): boolean => {
+    const urlChanged = prowlarrUrl.trim() !== originalProwlarrUrl.trim();
+    const apiKeyChanged = !prowlarrApiKey.startsWith('••••') &&
+      prowlarrApiKey !== originalProwlarrApiKey;
+    return urlChanged || apiKeyChanged;
+  }, [prowlarrUrl, prowlarrApiKey, originalProwlarrUrl, originalProwlarrApiKey]);
+
+  /**
+   * Execute the actual Prowlarr connection test
+   */
+  const executeTest = async (shouldClearIndexers: boolean) => {
     setTesting(true);
     setTestResult(null);
 
@@ -46,14 +66,23 @@ export function useIndexersSettings({
 
       if (data.success) {
         onValidationChange(true);
-        setTestResult({
-          success: true,
-          message: `Connected to Prowlarr. Found ${data.indexers?.length || 0} indexers`,
-        });
 
-        // Refresh indexers from database if callback provided
-        if (onRefreshIndexers) {
-          await onRefreshIndexers();
+        if (shouldClearIndexers) {
+          onClearIndexers();
+          setTestResult({
+            success: true,
+            message: `Connected to Prowlarr. Found ${data.indexers?.length || 0} indexers. Previous indexer configurations have been removed — please re-add indexers from the new instance.`,
+          });
+        } else {
+          setTestResult({
+            success: true,
+            message: `Connected to Prowlarr. Found ${data.indexers?.length || 0} indexers`,
+          });
+
+          // Refresh indexers from database if callback provided
+          if (onRefreshIndexers) {
+            await onRefreshIndexers();
+          }
         }
       } else {
         onValidationChange(false);
@@ -74,9 +103,41 @@ export function useIndexersSettings({
     }
   };
 
+  /**
+   * Handle test connection click — shows confirmation if credentials changed
+   * and there are existing configured indexers.
+   */
+  const testConnection = async () => {
+    if (hasConnectionChanged() && configuredIndexersCount > 0) {
+      setShowConnectionChangeConfirm(true);
+      return;
+    }
+
+    await executeTest(false);
+  };
+
+  /**
+   * User confirmed the credential change — proceed with test and clear indexers on success
+   */
+  const confirmConnectionChange = async () => {
+    setShowConnectionChangeConfirm(false);
+    await executeTest(true);
+  };
+
+  /**
+   * User cancelled the credential change confirmation
+   */
+  const cancelConnectionChange = () => {
+    setShowConnectionChangeConfirm(false);
+  };
+
   return {
     testing,
     testResult,
     testConnection,
+    showConnectionChangeConfirm,
+    confirmConnectionChange,
+    cancelConnectionChange,
+    configuredIndexersCount,
   };
 }