style(Editor): 调整布局样式和缩略图按钮

优化编辑器中心区域的最大宽度和溢出处理
简化缩略图添加按钮的显示并调整宽度

src/views/Editor/Thumbnails/index2.vue

@@ -6,8 +6,8 @@
     v-contextmenu="contextmenusThumbnails"
   >
     <div class="add-slide">
-      <div class="btn" @click="createSlide()"><IconPlus class="icon" />添加幻灯片</div>
-      <!-- <Popover trigger="click" placement="bottom-start" v-model:value="presetLayoutPopoverVisible" center>
+      <div class="btn" @click="createSlide()"><IconPlus class="icon" /></div>
+      <!-- 添加幻灯片 <Popover trigger="click" placement="bottom-start" v-model:value="presetLayoutPopoverVisible" center>
         <template #content>
           <Templates 
             @select="slide => { createSlideByTemplate(slide); presetLayoutPopoverVisible = false }"
@@ -374,7 +374,7 @@ const contextmenusThumbnailItem = (): ContextmenuItem[] => {
 }
 .add-slide {
   height: 100%;
-  width: 50px;
+  width: 40px;
   font-size: 12px;
   display: flex;
   flex-shrink: 0;

src/views/Editor/index2.vue

@@ -121,6 +121,8 @@ usePasteEvent()
 .layout-content-center {
   flex: 1;
   transition: width 0.3s ease;
+  max-width: 100%;
+  overflow: hidden;
 }
 
 .layout-content-center .center-top {