Add SABnzbd Usenet/NZB integration and documentation

Introduces SABnzbd as a supported download client for Usenet/NZB alongside qBittorrent, including service implementation, setup wizard and admin settings UI updates, and protocol-specific job processor logic. Updates documentation, PRD, and database schema to support NZB downloads, adds comprehensive technical details and testing strategies, and fixes Audible integration issues related to search and ASIN extraction.

src/lib/integrations/prowlarr.service.ts

@@ -114,8 +114,10 @@ export class ProwlarrService {
         .map((result: ProwlarrSearchResult) => this.transformResult(result))
         .filter((result: TorrentResult | null) => result !== null) as TorrentResult[];
 
-      // Apply filters
-      let filtered = results;
+      // Filter by protocol based on configured download client
+      let filtered = await this.filterByProtocol(results);
+
+      // Apply additional filters
 
       if (filters?.minSeeders) {
         filtered = filtered.filter((r) => r.seeders >= (filters.minSeeders || 0));
@@ -293,6 +295,58 @@ export class ProwlarrService {
     return allResults;
   }
 
+  /**
+   * Filter results based on configured download client protocol
+   * If qBittorrent is configured: only return torrent results
+   * If SABnzbd is configured: only return NZB results
+   */
+  private async filterByProtocol(results: TorrentResult[]): Promise<TorrentResult[]> {
+    try {
+      // Get configured download client type
+      const { getConfigService } = await import('../services/config.service');
+      const config = await getConfigService();
+      const clientType = (await config.get('download_client_type')) || 'qbittorrent';
+
+      if (clientType === 'sabnzbd') {
+        // Filter for NZB results only
+        const filtered = results.filter(result => ProwlarrService.isNZBResult(result));
+        console.log(`[Prowlarr] Filtered ${results.length} results to ${filtered.length} NZB results for SABnzbd`);
+        return filtered;
+      } else {
+        // Filter for torrent results only (default)
+        const filtered = results.filter(result => !ProwlarrService.isNZBResult(result));
+        console.log(`[Prowlarr] Filtered ${results.length} results to ${filtered.length} torrent results for qBittorrent`);
+        return filtered;
+      }
+    } catch (error) {
+      console.error('[Prowlarr] Failed to filter by protocol, returning all results:', error);
+      return results; // Fallback: return unfiltered if config fails
+    }
+  }
+
+  /**
+   * Detect if a result is an NZB download (Usenet) or torrent (BitTorrent)
+   * Static method for protocol detection
+   */
+  static isNZBResult(result: TorrentResult): boolean {
+    const url = result.downloadUrl.toLowerCase();
+
+    // Check file extension
+    if (url.endsWith('.nzb')) {
+      return true;
+    }
+
+    // Check URL path
+    if (url.includes('/nzb/') || url.includes('&t=get')) {
+      return true;
+    }
+
+    // Check categories (3030 is audiobooks, but some indexers use Usenet-specific codes)
+    // Note: This is less reliable, so we prioritize URL patterns
+
+    return false;
+  }
+
   /**
    * Transform Prowlarr result to our TorrentResult format
    */