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/app/api/setup/test-download-client/route.ts

@@ -5,37 +5,80 @@
 
 import { NextRequest, NextResponse } from 'next/server';
 import { QBittorrentService } from '@/lib/integrations/qbittorrent.service';
+import { SABnzbdService } from '@/lib/integrations/sabnzbd.service';
 
 export async function POST(request: NextRequest) {
   try {
     const { type, url, username, password, disableSSLVerify } = await request.json();
 
-    if (!type || !url || !username || !password) {
+    if (!type || !url) {
       return NextResponse.json(
-        { success: false, error: 'All fields are required' },
+        { success: false, error: 'Type and URL are required' },
         { status: 400 }
       );
     }
 
-    if (type !== 'qbittorrent') {
+    if (type !== 'qbittorrent' && type !== 'sabnzbd') {
       return NextResponse.json(
-        { success: false, error: 'Only qBittorrent is currently supported' },
+        { success: false, error: 'Invalid client type. Must be qbittorrent or sabnzbd' },
         { status: 400 }
       );
     }
 
-    // Test connection with custom credentials
-    const version = await QBittorrentService.testConnectionWithCredentials(
-      url,
-      username,
-      password,
-      disableSSLVerify || false
+    // Validate required fields per client type
+    if (type === 'qbittorrent') {
+      if (!username || !password) {
+        return NextResponse.json(
+          { success: false, error: 'Username and password are required for qBittorrent' },
+          { status: 400 }
+        );
+      }
+
+      // Test qBittorrent connection
+      const version = await QBittorrentService.testConnectionWithCredentials(
+        url,
+        username,
+        password,
+        disableSSLVerify || false
+      );
+
+      return NextResponse.json({
+        success: true,
+        version,
+      });
+    } else if (type === 'sabnzbd') {
+      if (!password) {
+        return NextResponse.json(
+          { success: false, error: 'API key (password) is required for SABnzbd' },
+          { status: 400 }
+        );
+      }
+
+      // Test SABnzbd connection
+      const sabnzbd = new SABnzbdService(url, password, 'readmeabook', disableSSLVerify || false);
+      const result = await sabnzbd.testConnection();
+
+      if (!result.success) {
+        return NextResponse.json(
+          {
+            success: false,
+            error: result.error || 'Failed to connect to SABnzbd',
+          },
+          { status: 500 }
+        );
+      }
+
+      return NextResponse.json({
+        success: true,
+        version: result.version,
+      });
+    }
+
+    // Should never reach here
+    return NextResponse.json(
+      { success: false, error: 'Invalid client type' },
+      { status: 400 }
     );
-
-    return NextResponse.json({
-      success: true,
-      version,
-    });
   } catch (error) {
     console.error('[Setup] Download client test failed:', error);
     return NextResponse.json(