style: improve inline diff partial style (#3877)

Author: Ricbet

packages/ai-native/src/browser/widget/inline-stream-diff/inline-stream-diff.module.less

@@ -43,6 +43,9 @@
     border-radius: 4px;
     overflow: hidden;
     margin-right: 10px;
+    max-height: 18px;
+    height: 18px;
+    align-items: center;
   }
 
   .btn {