Admin requests: paginated API & UI overhaul

Add a paginated Admin Requests API and fully refactor the admin requests UI to support filtering, sorting, pagination, and URL state.

- New API: src/app/api/admin/requests/route.ts implements paginated, searchable, filterable, and sortable request listing with proper relation includes and pagination metadata.
- Frontend: RecentRequestsTable rewritten to fetch via SWR (authenticatedFetcher), read/write URL query params, debounce search, support status/user filters, sortable columns, page size selector, and full pagination UI; added loading/error states and toast feedback for actions.
- Admin page updated to use Suspense and the new RecentRequestsTable (component now fetches its own data).
- Settings: deprecated single download-client PUT route now maps updates into the new multi-client format (download_clients JSON), logs deprecation, and invalidates download client manager; settings GET now reads multi-client config for backward compatibility.
- Processors: monitor-download and retry-failed-imports updated to use the download-client-manager and new PathMappingConfig shape for path mapping logic.
- Minor API/schema updates: request-with-torrent schema extended (indexerId, infoUrl, protocol) and setup complete no longer writes legacy path keys.
- Tests updated to reflect API and processor changes.

This change centralizes request management on the server, modernizes the UI for large datasets, and migrates download client settings toward a multi-client configuration while keeping backward compatibility.

src/app/api/audiobooks/request-with-torrent/route.ts

@@ -35,12 +35,15 @@ const RequestWithTorrentSchema = z.object({
     seeders: z.number().optional(), // Optional for NZB/Usenet results
     leechers: z.number().optional(), // Optional for NZB/Usenet results
     indexer: z.string(),
+    indexerId: z.number().optional(), // Prowlarr indexer ID
     downloadUrl: z.string(),
+    infoUrl: z.string().optional(), // Link to indexer's info page
     publishDate: z.string().transform((str) => new Date(str)),
     infoHash: z.string().optional(),
     format: z.enum(['M4B', 'M4A', 'MP3', 'OTHER']).optional(),
     bitrate: z.string().optional(),
     hasChapters: z.boolean().optional(),
+    protocol: z.enum(['torrent', 'usenet']).optional(), // Protocol from Prowlarr API
   }),
 });