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/requests/InteractiveTorrentSearchModal.test.tsx

@@ -13,6 +13,10 @@ const searchByRequestMock = vi.hoisted(() => vi.fn());
 const selectTorrentMock = vi.hoisted(() => vi.fn());
 const searchByAudiobookMock = vi.hoisted(() => vi.fn());
 const requestWithTorrentMock = vi.hoisted(() => vi.fn());
+const searchEbooksMock = vi.hoisted(() => vi.fn());
+const selectEbookMock = vi.hoisted(() => vi.fn());
+const searchEbooksByAsinMock = vi.hoisted(() => vi.fn());
+const selectEbookByAsinMock = vi.hoisted(() => vi.fn());
 
 vi.mock('@/lib/hooks/useRequests', () => ({
   useInteractiveSearch: () => ({
@@ -35,6 +39,26 @@ vi.mock('@/lib/hooks/useRequests', () => ({
     isLoading: false,
     error: null,
   }),
+  useInteractiveSearchEbook: () => ({
+    searchEbooks: searchEbooksMock,
+    isLoading: false,
+    error: null,
+  }),
+  useSelectEbook: () => ({
+    selectEbook: selectEbookMock,
+    isLoading: false,
+    error: null,
+  }),
+  useInteractiveSearchEbookByAsin: () => ({
+    searchEbooks: searchEbooksByAsinMock,
+    isLoading: false,
+    error: null,
+  }),
+  useSelectEbookByAsin: () => ({
+    selectEbook: selectEbookByAsinMock,
+    isLoading: false,
+    error: null,
+  }),
 }));
 
 const baseResult = {