feat(submit): fold slide cover into multi-select image picker

Match the featured cover buttons row to the reference theme: drop the
dedicated slide button, let the icon-only image picker select multiple
images into a slide cover (single pick stays an image cover), and align
the loaded-state visibility matrix.

assets/js/front-submit.js

@@ -88,6 +88,7 @@
     isDirty: false,
     isSubmitting: false,
     featured: { type: '', data: {} },
+    featuredOptions: {},
 
     init: function () {
       this.form = document.getElementById('aksrt-submit-form');
@@ -387,6 +388,7 @@
         if (args && args.type) {
           this.featured = { type: args.type, data: args.data || {} };
         }
+        this.featuredOptions = (args && args.options) || {};
       } catch (e) {}
     },
 
@@ -487,28 +489,30 @@
           return;
         }
         if (act === 'image') {
+          // 与服务端 featured 校验对齐：多选（或仅有幻灯片权限时的单选）存为幻灯片封面，其余存为图片封面。
+          var coverOptions = self.featuredOptions || {};
+          var slideEnabled = !!coverOptions.slide;
+          var imageAllowed = !!coverOptions.image;
           self.openMediaPicker({
             type: 'image',
-            multiple: false,
-            allowExternal: false,
-            onSelect: function (item) {
-              if (!item) return;
-              self.setFeatured('image', { url: item.url || '', id: item.attachment_id || item.id || 0 });
-            },
-          });
-          return;
-        }
-        if (act === 'slide') {
-          self.openMediaPicker({
-            type: 'image',
-            multiple: true,
-            maxItems: 30,
+            multiple: slideEnabled,
+            maxItems: slideEnabled ? 30 : 1,
             allowExternal: false,
             onSelect: function (items) {
-              var slides = (Array.isArray(items) ? items : []).map(function (item) {
-                return { url: item.url || '', id: item.attachment_id || item.id || 0 };
-              }).filter(function (item) { return item.url || item.id; });
-              if (slides.length) self.setFeatured('slide', slides);
+              var list = Array.isArray(items) ? items : [items];
+              var slides = [];
+              list.forEach(function (item) {
+                if (!item) return;
+                var url = item.url || '';
+                var id = item.attachment_id || item.id || 0;
+                if (url || id) slides.push({ url: url, id: id });
+              });
+              if (!slides.length) return;
+              if (slides.length > 1 || (slideEnabled && !imageAllowed)) {
+                self.setFeatured('slide', slides);
+                return;
+              }
+              self.setFeatured('image', slides[0]);
             },
           });
           return;