Add ASIN/ISBN fields to library and improve matching

Introduces `asin` and `isbn` fields to the PlexLibrary schema and database, with migration and indexing for fast lookups. Updates scan and recently-added processors to persist ASIN/ISBN from both Plex and Audiobookshelf backends. Enhances matching logic to prioritize exact ASIN matches using the new fields, improving match accuracy for Audiobookshelf users. Also includes minor improvements: fixes cover art handling for cached thumbnails, adds download URL validation in Prowlarr and qBittorrent integrations, and updates documentation to reflect these changes.

prisma/migrations/20251222140111_add_asin_isbn_to_library/migration.sql

@@ -0,0 +1,9 @@
+-- AlterTable
+ALTER TABLE "plex_library" ADD COLUMN "asin" TEXT,
+ADD COLUMN "isbn" TEXT;
+
+-- CreateIndex
+CREATE INDEX "plex_library_asin_idx" ON "plex_library"("asin");
+
+-- CreateIndex
+CREATE INDEX "plex_library_isbn_idx" ON "plex_library"("isbn");

prisma/schema.prisma

@@ -100,9 +100,10 @@ model AudibleCache {
 }
 
 // ============================================================================
-// PLEX LIBRARY TABLE
-// Pure Plex library content - What's actually in your Plex server
-// No Audible data - just Plex metadata and file info
+// LIBRARY CACHE TABLE (plex_library for backward compatibility)
+// Universal library content - Works with Plex or Audiobookshelf backends
+// Stores complete metadata including ASIN/ISBN for accurate matching
+// No Audible data - just library backend metadata and file info
 // ============================================================================
 model PlexLibrary {
   id            String    @id @default(uuid())
@@ -117,6 +118,10 @@ model PlexLibrary {
   year          Int?
   userRating    Decimal?  @map("user_rating") @db.Decimal(3, 1) // User's rating (0-10 scale from Plex)
 
+  // Universal identifiers (works for both Plex and Audiobookshelf)
+  asin          String?   // Audible ASIN - extracted from Plex GUID or stored directly from ABS
+  isbn          String?   // ISBN (10 or 13) - for additional matching capability
+
   // File information
   filePath      String?   @map("file_path") @db.Text
   thumbUrl      String?   @map("thumb_url") @db.Text // Plex thumbnail URL
@@ -133,6 +138,8 @@ model PlexLibrary {
   @@index([title])
   @@index([author])
   @@index([plexLibraryId])
+  @@index([asin])
+  @@index([isbn])
   @@map("plex_library")
 }