lint(handlers): Use strings.EqualFold for case-insensitive comparison

Fix SA6005 staticcheck warning in OPDS handler

internal/handlers/opds.go

@@ -106,7 +106,7 @@ func (h *OPDSHandler) GetDeviceCatalog(c echo.Context) error {
 	if includeFormat != "" {
 		filteredItems := []database.ListMediaItemsByLibraryRow{}
 		for _, item := range allItems {
-			if strings.ToLower(item.FormatGroup) == strings.ToLower(includeFormat) {
+			if strings.EqualFold(item.FormatGroup, includeFormat) {
 				filteredItems = append(filteredItems, item)
 			}
 		}