perf: update placeholder picture.

src/views/interface/ThemeList.vue

@@ -24,7 +24,7 @@
               <div class="theme-thumb">
                 <img
                   :alt="item.name"
-                  :src="item.screenshots"
+                  :src="item.screenshots || '/images/placeholder.jpg'"
                   loading="lazy"
                 >
               </div>

src/views/post/components/PostSettingDrawer.vue

@@ -156,7 +156,7 @@
             <div class="post-thumb">
               <img
                 class="img"
-                :src="selectedPost.thumbnail || '/images/placeholder.png'"
+                :src="selectedPost.thumbnail || '/images/placeholder.jpg'"
                 @click="()=>this.thumbDrawerVisible=true"
               >
               <a-button

src/views/sheet/components/SheetSettingDrawer.vue

@@ -73,7 +73,7 @@
             <div class="sheet-thumb">
               <img
                 class="img"
-                :src="selectedSheet.thumbnail || '/images/placeholder.png'"
+                :src="selectedSheet.thumbnail || '/images/placeholder.jpg'"
                 @click="()=>this.thumbDrawerVisible = true"
               >
               <a-button

src/views/sheet/internal/PhotoList.vue

@@ -130,7 +130,7 @@
           >
             <div class="photo-detail-img">
               <img
-                :src="photo.url || '/images/placeholder.png'"
+                :src="photo.url || '/images/placeholder.jpg'"
                 @click="showThumbDrawer"
                 style="width: 100%;"
               >