feat: artalk 支持點擊打開大圖

feat: 設置了隨系統而切換淺色和深色模式後，評論和 mermaind 也會跟隨切換顏色
feat: artalk 最新評論，從 artalk 配置讀取頭像 CDN 和默認頭像
fix: 修復代碼塊在未展開時，點擊複製按鈕，無法複製的 bug
improvement: 代碼和性能優化
improvement: artalk 獲取評論數，由 LoadCountWidget 改為 loadCountWidget

layout/includes/third-party/comments/utterances.pug

@@ -12,10 +12,10 @@ script.
     document.getElementById('utterances-wrap').insertAdjacentElement('afterbegin',ele)
   }
 
-  function utterancesTheme () {
+  function utterancesTheme (theme) {
     const iframe = document.querySelector('.utterances-frame')
     if (iframe) {
-      const theme = document.documentElement.getAttribute('data-theme') === 'dark' ? '#{theme.utterances.dark_theme}' : '#{theme.utterances.light_theme}'
+      const theme = theme === 'dark' ? '#{theme.utterances.dark_theme}' : '#{theme.utterances.light_theme}'
       const message = {
         type: 'set-theme',
         theme: theme
@@ -24,6 +24,8 @@ script.
     }
   }
 
+  btf.addModeChange('utterances', utterancesTheme)
+
   if ('!{theme.comments.use[0]}' === 'Utterances' || !!{theme.comments.lazyload}) {
     if (!{theme.comments.lazyload}) btf.loadComment(document.getElementById('utterances-wrap'), loadUtterances)
     else loadUtterances()