Add extensible notification providers + UI/API

Introduce a provider-based notification system and wire it through the API and admin UI. Added INotificationProvider + notification service implementation and providers (apprise, discord, ntfy, pushover), plus a GET /api/admin/notifications/providers endpoint to expose provider metadata. Refactored code to use provider type strings (removed enum coupling), updated masking/encryption calls, and simplified the test notification endpoint to accept backendId or type+config and call sendToBackend directly.

UI: NotificationsTab now fetches provider metadata and renders provider cards and dynamic config forms (fields driven by provider metadata). Added config field rendering, improved backend cards, and edit/delete actions.

APIs: New providers route, updated admin notification CRUD routes to validate provider types dynamically, updated test route schema. Added download-client categories POST API to fetch categories from clients and wired postImportCategory handling in download-client routes.

Other notable changes: BookDate now fetches Claude models dynamically from Anthropic's Models API; added paginated model fetch helper. Added ALLOW_WEAK_PASSWORD flag exposure to auth providers and password change logic. Doc updates and various tests added/updated. File-organization doc clarifies EPERM fix using stream-based copy.

src/app/api/audiobooks/search-torrents/route.ts

@@ -86,7 +86,6 @@ export async function POST(request: NextRequest) {
 
       // Search Prowlarr for each group and combine results
       const prowlarr = await getProwlarrService();
-      const searchQuery = title; // Title only - cast wide net
       const allResults = [];
 
       for (let i = 0; i < groups.length; i++) {
@@ -94,7 +93,7 @@ export async function POST(request: NextRequest) {
         logger.debug(`Searching group ${i + 1}/${groups.length}: ${getGroupDescription(group)}`);
 
         try {
-          const groupResults = await prowlarr.search(searchQuery, {
+          const groupResults = await prowlarr.searchWithVariations(title, author, {
             categories: group.categories,
             indexerIds: group.indexerIds,
             maxResults: 100, // Limit per group