fix(KB-258): add overflow auto to file editor textarea

- Add overflow: auto to file-editor-textarea CSS class for scroll support
- Ensure long file content is scrollable within the editor viewport

packages/dashboard/app/styles.css

@@ -6301,6 +6301,7 @@ html .column.drag-over * {
   border: none;
   outline: none;
   resize: none;
+  overflow: auto;
   white-space: pre;
   overflow-wrap: normal;
   tab-size: 2;