write(css): splitter 放 sidebar 后而不是前；display:none 的 mobile-bar 不占 grid cell 之前算错了顺序

apps/write/frontend/src/App.vue

@@ -274,8 +274,6 @@ onMounted(() => {
 
     <div class="sidebar-backdrop" @click="drawerOpen = false"></div>
 
-    <div class="splitter splitter-main" @mousedown="startDrag($event, 'sidebar')" title="拖动调整侧栏宽度"></div>
-
     <aside class="sidebar">
       <div class="sidebar-header">
         <h1>✍ write</h1>
@@ -298,6 +296,8 @@ onMounted(() => {
       </div>
     </aside>
 
+    <div class="splitter splitter-main" @mousedown="startDrag($event, 'sidebar')" title="拖动调整侧栏宽度"></div>
+
     <main class="workspace">
       <div class="editor-pane">
         <div class="title-row">