SABnzbd path mapping + ASIN-based request deletion

Add bidirectional path mapping and complete_dir-aware category sync to the SABnzbd integration. Introduces PathMapper usage, complete_dir extraction, calculateCategoryPath(), and ensureCategory() logic to choose empty/relative/absolute category paths; ensureCategory is invoked before adding NZBs. Update singleton factory to load download_dir and path-mapping config from DownloadClientManager and recreate the service when config is not loaded. Make DownloadClientManager pass path-mapping config into the SABnzbd service. Change request deletion to remove plex_library records by ASIN (deleteMany) with a fallback to exact title/author matches so availability checks and deletions are consistent. Update documentation and tests to reflect the new behavior and APIs.

tests/components/audiobooks/AudiobookDetailsModal.test.tsx

@@ -12,6 +12,8 @@ import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest';
 const useAuthMock = vi.hoisted(() => vi.fn());
 const useAudiobookDetailsMock = vi.hoisted(() => vi.fn());
 const createRequestMock = vi.hoisted(() => vi.fn());
+const fetchEbookMock = vi.hoisted(() => vi.fn());
+const revalidateEbookStatusMock = vi.hoisted(() => vi.fn());
 
 vi.mock('@/contexts/AuthContext', () => ({
   useAuth: () => useAuthMock(),
@@ -23,6 +25,11 @@ vi.mock('@/lib/hooks/useAudiobooks', () => ({
 
 vi.mock('@/lib/hooks/useRequests', () => ({
   useCreateRequest: () => ({ createRequest: createRequestMock, isLoading: false }),
+  useEbookStatus: () => ({
+    ebookStatus: { ebookSourcesEnabled: false, hasActiveEbookRequest: false },
+    revalidate: revalidateEbookStatusMock,
+  }),
+  useFetchEbookByAsin: () => ({ fetchEbook: fetchEbookMock, isLoading: false }),
 }));
 
 vi.mock('@/components/requests/InteractiveTorrentSearchModal', () => ({