Potential fix for pull request finding

Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>

internal/library/library.go

@@ -97,17 +97,33 @@ func (s *Service) FindBook(id string) (*Book, error) {
 }
 
 func (s *Service) CoverBytes(id string) ([]byte, string, error) {
-	book, err := s.FindBook(id)
+	if id == "" {
+		return nil, "", nil
+	}
+
+	entries, err := os.ReadDir(s.booksDir)
 	if err != nil {
+		if os.IsNotExist(err) {
+			return nil, "", nil
+		}
 		return nil, "", err
 	}
-	if book == nil {
-		return nil, "", nil
+
+	for _, e := range entries {
+		if e.IsDir() {
+			continue
+		}
+		ext := strings.ToLower(filepath.Ext(e.Name()))
+		if ext != ".epub" {
+			continue
+		}
+		if stableID(e.Name()) != id {
+			continue
+		}
+		return readEPUBCover(filepath.Join(s.booksDir, e.Name()))
 	}
-	if book.Format != "epub" {
-		return nil, "", nil
-	}
-	return readEPUBCover(book.Path)
+
+	return nil, "", nil
 }
 
 func stableID(input string) string {