chore: 升級版本至 5.5.3 並合併開發分支功能更新

主要更新內容：
- feat: 網站背景支援隨機數組配置，可從多個背景中隨機選擇
- feat: 增加文章分頁封面配置 pagination_cover 選項
- improvement: 優化代碼高亮工具複製按鈕的位置計算和邊界檢查
- improvement: 優化 Pjax 載入，script 標籤新增 defer 屬性
- improvement: 優化相關文章算法，提升性能並改進排序邏輯
- improvement: 優化側邊欄歸檔和分類模塊的性能
- improvement: 改善 TOC 滾動檢測和位置計算
- improvement: 優化 Umami Analytics 數據處理邏輯
- fix: 修復代碼塊工具欄圖標對齊和樣式問題
- fix: 修復夜間模式下圖片亮度調整
- fix: 修復閱讀模式按鈕樣式和功能
- chore: 更新多個依賴套件版本（algolia, fancybox, katex, mermaid, waline 等）

此次合併解決了所有衝突並整合了開發分支的所有新功能和優化。

_config.yml

@@ -91,7 +91,8 @@ category_per_img:
 footer_img: false
 
 # Website Background
-# Can set it to color or image url
+# Can set it to color, image URL or an array containing colors and/or image URLs
+# If an array is provided, a random background will be selected from the array on each load
 background:
 
 cover:

layout/includes/additional-js.pug

@@ -52,7 +52,7 @@ div
     != partial("includes/third-party/umami_analytics", {}, { cache: true })
 
   if theme.busuanzi.site_uv || theme.busuanzi.site_pv || theme.busuanzi.page_pv
-    script(async data-pjax src=url_for(theme.asset.busuanzi) || '//busuanzi.ibruce.info/busuanzi/2.3/busuanzi.pure.mini.js')
+    script(async data-pjax src=theme.asset.busuanzi ? url_for(theme.asset.busuanzi) : '//busuanzi.ibruce.info/busuanzi/2.3/busuanzi.pure.mini.js')
 
   != partial('includes/third-party/search/index', {}, { cache: true })
 

layout/includes/layout.pug

@@ -13,7 +13,29 @@ html(lang=config.language data-theme=theme.display_mode class=htmlClassHideAside
     !=partial('includes/loading/index', {}, {cache: true})
 
     if theme.background
-      #web_bg(style=getBgPath(theme.background))
+      if !Array.isArray(theme.background)
+        #web_bg.bg-animation(style=getBgPath(theme.background))
+      else
+        #web_bg.bg-animation
+        - const bgStyleArr = theme.background.map(getBgPath)
+        script.
+          (() => {
+            const arr = !{JSON.stringify(bgStyleArr)}
+            const webBgDiv = document.getElementById('web_bg')
+
+            const setRandomBg = () => {
+              webBgDiv.style = arr[Math.floor(Math.random() * arr.length)]
+              requestAnimationFrame(() => webBgDiv.classList.add('bg-animation'))
+            }
+
+            document.addEventListener('pjax:send', () => {
+              webBgDiv.style = ''
+              webBgDiv.classList.remove('bg-animation')
+            })
+
+            document.addEventListener('pjax:complete', setRandomBg)
+            document.addEventListener('DOMContentLoaded', setRandomBg)
+          })()
 
     !=partial('includes/sidebar', {}, {cache: true})