feat(audiobooks): library-type recognizers for scanner dispatch

isAudiobookLibraryType and isPodcastLibraryType match singular and
plural forms case-insensitively, mirroring isMovieLibraryType. Used by
upcoming scanner walk branches (Task 4) that filter audio files into
audiobook and podcast libraries.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

internal/scanner/scanner.go

@@ -215,6 +215,22 @@ func isMovieLibraryType(libraryType string) bool {
 		return false
 	}
 }
+func isAudiobookLibraryType(libraryType string) bool {
+	switch strings.ToLower(strings.TrimSpace(libraryType)) {
+	case "audiobook", "audiobooks":
+		return true
+	default:
+		return false
+	}
+}
+func isPodcastLibraryType(libraryType string) bool {
+	switch strings.ToLower(strings.TrimSpace(libraryType)) {
+	case "podcast", "podcasts":
+		return true
+	default:
+		return false
+	}
+}
 
 func canonicalWalkPath(path string) (string, error) {
 	resolved, err := filepath.EvalSymlinks(path)

internal/scanner/scanner_test.go

@@ -129,3 +129,43 @@ func testStringSliceContains(values []string, target string) bool {
 	}
 	return false
 }
+
+func TestIsAudiobookLibraryType(t *testing.T) {
+	cases := []struct {
+		in   string
+		want bool
+	}{
+		{"audiobooks", true},
+		{"audiobook", true},
+		{"Audiobook", true},
+		{"  AUDIOBOOKS  ", true},
+		{"movies", false},
+		{"series", false},
+		{"", false},
+	}
+	for _, tc := range cases {
+		if got := isAudiobookLibraryType(tc.in); got != tc.want {
+			t.Errorf("isAudiobookLibraryType(%q) = %v, want %v", tc.in, got, tc.want)
+		}
+	}
+}
+
+func TestIsPodcastLibraryType(t *testing.T) {
+	cases := []struct {
+		in   string
+		want bool
+	}{
+		{"podcasts", true},
+		{"podcast", true},
+		{"Podcast", true},
+		{"  PODCASTS  ", true},
+		{"series", false},
+		{"audiobooks", false},
+		{"", false},
+	}
+	for _, tc := range cases {
+		if got := isPodcastLibraryType(tc.in); got != tc.want {
+			t.Errorf("isPodcastLibraryType(%q) = %v, want %v", tc.in, got, tc.want)
+		}
+	}
+}