i18n: add longPressImageSave string used by the image lightbox

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/i18n.tsx

@@ -45,6 +45,7 @@ const zhDict: Dict = {
   downloading: "下载中…",
   downloadOk: "下载完成",
   downloadFail: "下载失败，请重试",
+  longPressImageSave: "长按图片保存到相册",
   showMore: "展开全部",
   showLess: "收起全部",
   share: "分享",
@@ -173,6 +174,7 @@ const enDict: Dict = {
   downloading: "Downloading…",
   downloadOk: "Download complete",
   downloadFail: "Download failed, please retry",
+  longPressImageSave: "Long-press image to save",
   showMore: "Show all",
   showLess: "Show less",
   share: "Share",