Add e-book sidecar integration and improve request handling

Introduces optional e-book sidecar downloads from Anna's Archive, including admin UI, settings API, FlareSolverr integration, and documentation. Enhances request creation logic to prevent duplicate downloads by checking for 'downloaded' and 'available' statuses, updates UI to reflect processing state, and adds SABnzbd support to download and cleanup flows. Also updates ranking algorithm documentation and improves cache invalidation for recent requests.

src/app/admin/components/RecentRequestsTable.tsx

@@ -102,6 +102,9 @@ export function RecentRequestsTable({ requests }: RecentRequestsTableProps) {
       await mutate('/api/admin/requests/recent');
       await mutate('/api/admin/metrics');
 
+      // Invalidate audiobook caches to update request status on home/search pages
+      await mutate((key) => typeof key === 'string' && key.includes('/api/audiobooks'));
+
       // Close dialog
       setShowDeleteConfirm(false);
       setSelectedRequest(null);