ui: place preview fullscreen control before close

Swap only the fullscreen and close button order in preview toolbars, including the BHA proofreading toolbar. No backend, data, index, configuration or CSS changes.

static/app.js

@@ -1206,8 +1206,8 @@ async function openPreview(docId, keyword, options = {}) {
           <div class="preview-path">${escapeHTML(data.source)} / ${escapeHTML(data.path)}</div>
         </div>
         <div class="preview-tools">
-          <button type="button" class="icon-btn-sm" data-action="close-preview" aria-label="关闭预览">×</button>
           ${previewFullscreenButtonHTML()}
+          <button type="button" class="icon-btn-sm" data-action="close-preview" aria-label="关闭预览">×</button>
           <button type="button" class="icon-btn-sm preview-theme-btn" data-action="toggle-preview-theme" aria-label="${STATE.isDark ? "切换到白天模式" : "切换到黑夜模式"}" title="${STATE.isDark ? "白天模式" : "黑夜模式"}">${themeIcon(STATE.isDark)}</button>
         </div>
       </div>