fix: banner移入content-wrapper，标签栏下方直接是两栏布局

renderer/index.html

@@ -84,13 +84,6 @@
       </button>
     </div>
 
-    <!-- External modification banner -->
-    <div id="modified-banner" class="hidden">
-      <span>文件已被外部程序修改</span>
-      <button id="btn-reload" class="banner-btn">重新加载</button>
-      <button id="btn-dismiss" class="banner-btn">忽略</button>
-    </div>
-
     <!-- Workspace: Sidebar + Main Content -->
     <div id="workspace">
       <!-- Sidebar -->
@@ -108,6 +101,13 @@
 
       <!-- Main content area -->
       <div id="main-content">
+      <div id="content-wrapper">
+      <!-- External modification banner -->
+      <div id="modified-banner" class="hidden">
+        <span>文件已被外部程序修改</span>
+        <button id="btn-reload" class="banner-btn">重新加载</button>
+        <button id="btn-dismiss" class="banner-btn">忽略</button>
+      </div>
       <!-- Editor panel -->
       <div id="editor-panel">
         <!-- Search & Replace Bar -->
@@ -144,6 +144,7 @@
       <div id="preview-panel">
         <div id="preview" class="markdown-body"></div>
       </div>
+      </div>
 
       <!-- Welcome screen -->
       <div id="welcome-screen">

renderer/renderer.js

@@ -17,6 +17,7 @@
   const editorPanel = document.getElementById('editor-panel');
   const previewPanel = document.getElementById('preview-panel');
   const mainContent = document.getElementById('main-content');
+  const contentWrapper = document.getElementById('content-wrapper');
   const tabList = document.getElementById('tab-list');
 
   // Sidebar
@@ -822,7 +823,7 @@
 
     document.addEventListener('mousemove', (e) => {
       if (!isResizing) return;
-      const rect = mainContent.getBoundingClientRect();
+      const rect = contentWrapper.getBoundingClientRect();
       const pct = Math.max(20, Math.min(80, ((e.clientX - rect.left) / rect.width) * 100));
       editorPanel.style.flex = `0 0 ${pct}%`;
       previewPanel.style.flex = `0 0 ${100 - pct}%`;

renderer/style.css

@@ -308,11 +308,20 @@ html, body {
 #main-content {
   flex: 1;
   display: flex;
+  flex-direction: column;
   overflow: hidden;
   position: relative;
   min-width: 0;
 }
 
+#content-wrapper {
+  flex: 1;
+  display: flex;
+  flex-direction: row;
+  overflow: hidden;
+  min-height: 0;
+}
+
 /* ===== Editor Panel ===== */
 #editor-panel {
   flex: 1;