fix(submit): render slide cover preview as a real swiper

Replace the static first-image preview with the reference theme's
.new-swiper contract (loop + autoplay + prev/next + pagination) in both
the server-rendered box and the JS re-render, and run auto_fun for
slide covers so new_swiper initializes them.

assets/js/front-submit.js

@@ -436,10 +436,21 @@
       if (t === 'image' && d.url) {
         html = '<img src="' + escapeHtml(d.url) + '" alt="">';
       } else if (t === 'slide' && Array.isArray(d) && d[0] && d[0].url) {
+        // 与参考主题一致：幻灯片封面渲染真实 swiper，由 auto_fun 里的 new_swiper 初始化。
+        var slideImgs = d
+          .filter(function (item) { return item && item.url; })
+          .map(function (item) {
+            return '<div class="swiper-slide"><img src="' + escapeHtml(item.url) + '" alt=""></div>';
+          })
+          .join('');
         html =
-          '<img src="' +
-          escapeHtml(d[0].url) +
-          '" alt=""><span class="featured-type-badge"><i class="fa fas fa-image"></i></span>';
+          '<div class="new-swiper scale-height" data-loop="true" data-autoplay="true" data-interval="2000" style="--scale-height:50%;">' +
+          '<div class="swiper-wrapper">' + slideImgs + '</div>' +
+          '<div class="swiper-button-prev"></div>' +
+          '<div class="swiper-button-next"></div>' +
+          '<div class="swiper-pagination"></div>' +
+          '</div>' +
+          '<span class="featured-type-badge"><i class="fa fas fa-image"></i></span>';
       } else if (t === 'video') {
         html =
           '<div class="new-dplayer dplayer-scale-height" style="--scale-height:50%;" video-url="' +
@@ -453,7 +464,7 @@
       }
       this.destroyFeaturedPlayer(preview);
       preview.innerHTML = html;
-      if (t === 'video' && typeof window.auto_fun === 'function') {
+      if ((t === 'video' || t === 'slide') && typeof window.auto_fun === 'function') {
         window.auto_fun();
       }
       var clearBtn = qs('[data-featured-action="close"]');