feat(submit): add video cover picker with playable video preview

Featured video preview now renders a real DPlayer (video-url/video-pic)
like the reference theme instead of a static image, so the cover video
plays on the submit page. Top-right bar gains the video-cover button
shown only when a video cover is loaded; backend honors pic_id and no
longer deletes the thumbnail before cover validation. Drop dead i18n
keys and data-can-* attributes.

assets/css/frontend/pages/submit.css

@@ -498,23 +498,13 @@ body.aksrt-editor-media-open {
   display: none;
 }
 
-.featured-edit .featured-preview > img,
-.featured-edit .featured-video-placeholder {
+.featured-edit .featured-preview > img {
   display: block;
   width: 100%;
   aspect-ratio: 2 / 1;
   object-fit: cover;
 }
 
-.featured-edit .featured-video-placeholder {
-  display: flex;
-  align-items: center;
-  justify-content: center;
-  flex-direction: column;
-  gap: 8px;
-  color: var(--muted-2-color, #999);
-}
-
 .featured-edit .featured-type-badge {
   position: absolute;
   right: 12px;
@@ -557,6 +547,14 @@ body.aksrt-editor-media-open {
   font-size: 1em;
 }
 
+.featured-edit .btns-full .btn-video-pic {
+  display: none;
+}
+
+.featured-loaded.video .btns-full .btn-video-pic {
+  display: inline-flex;
+}
+
 .featured-loaded.image .btn-video,
 .featured-loaded.image .btn-slide,
 .featured-loaded.slide .btn-video,

assets/js/front-submit.js

@@ -400,6 +400,22 @@
       this.isDirty = true;
     },
 
+    destroyFeaturedPlayer: function (preview) {
+      var old = qs('.new-dplayer', preview);
+      if (!old || !window.jQuery) {
+        return;
+      }
+      var dp = window.jQuery(old).data('dplayer');
+      if (dp) {
+        if (typeof dp.pause === 'function') {
+          dp.pause();
+        }
+        if (typeof dp.destroy === 'function') {
+          dp.destroy();
+        }
+      }
+    },
+
     renderFeaturedPreview: function () {
       var preview = qs('[data-featured-preview]');
       if (!preview) {
@@ -424,12 +440,20 @@
           '" alt=""><span class="featured-type-badge"><i class="fa fas fa-image"></i></span>';
       } else if (t === 'video') {
         html =
-          (d.pic
-            ? '<img src="' + escapeHtml(d.pic) + '" alt="">'
-            : '<div class="featured-video-placeholder"><i class="fa fas fa-play"></i></div>') +
+          '<div class="new-dplayer dplayer-scale-height" style="--scale-height:50%;" video-url="' +
+          escapeHtml(d.url || '') +
+          '" video-pic="' +
+          escapeHtml(d.pic || '') +
+          '"><div class="graphic" style="padding-bottom:50%;">' +
+          '<div class="abs-center text-center"><i class="fa fas fa-play-circle fa-4x muted-3-color opacity5" aria-hidden="true"></i></div>' +
+          '</div></div>' +
           '<span class="featured-type-badge"><i class="fa fas fa-video"></i></span>';
       }
+      this.destroyFeaturedPlayer(preview);
       preview.innerHTML = html;
+      if (t === 'video' && typeof window.auto_fun === 'function') {
+        window.auto_fun();
+      }
       var clearBtn = qs('[data-featured-action="close"]');
       if (clearBtn) {
         clearBtn.hidden = !t || t === 'close';
@@ -489,6 +513,27 @@
           });
           return;
         }
+        if (act === 'video_pic') {
+          var current = self.featured;
+          if (current.type !== 'video' || !current.data || !current.data.url) {
+            return;
+          }
+          self.openMediaPicker({
+            type: 'image',
+            multiple: false,
+            allowExternal: false,
+            title: i18n.setVideoCoverTitle || '为视频设置首图封面',
+            onSelect: function (cover) {
+              self.setFeatured('video', {
+                url: current.data.url,
+                pic: cover && cover.url ? cover.url : '',
+                pic_id: cover ? (cover.attachment_id || cover.id || 0) : 0,
+                id: current.data.id || 0,
+              });
+            },
+          });
+          return;
+        }
         if (act === 'video') {
           self.openMediaPicker({
             type: 'video',
@@ -509,7 +554,7 @@
                   type: 'image',
                   multiple: false,
                   allowExternal: false,
-                  title: i18n.pickVideoCover || '选择视频封面（可选）',
+                  title: i18n.setVideoCoverTitle || '为视频设置首图封面',
                   onSelect: function (cover) {
                     self.setFeatured('video', {
                       url: video.url,