fix: code editor style (#9667)

* fix(markdown): 修复cm-announced导致滚动条出现大量空白区域的问题

* fix(CodeBlockView): 修复自动补全被隐藏的问题

* revert: preserve code viewer border radius

---------

Co-authored-by: one <wangan.cs@gmail.com>

src/renderer/src/assets/styles/markdown.scss

@@ -367,4 +367,9 @@ mjx-container {
       white-space: pre-wrap;
     }
   }
+
+  .cm-announced {
+    position: absolute;
+    display: none;
+  }
 }

src/renderer/src/components/CodeBlockView/view.tsx

@@ -370,7 +370,10 @@ const SplitViewWrapper = styled.div<{ $isSpecialView: boolean; $isSplitView: boo
   &:not(:has(+ [class*='Container'])) {
     // 特殊视图的 header 会隐藏，所以全都使用圆角
     border-radius: ${(props) => (props.$isSpecialView ? '8px' : '0 0 8px 8px')};
-    overflow: hidden;
+    .code-viewer {
+      border-radius: 0 0 8px 8px;
+      overflow: hidden;
+    }
   }
 
   // 在 split 模式下添加中间分隔线