fix(KB-254): fix textarea height in file editor

- Add flex: 1 to allow textarea to fill available space in flex container
- Add min-height: 0 to prevent flexbox min-height constraints from limiting growth

packages/dashboard/app/styles.css

@@ -6273,6 +6273,8 @@ html .column.drag-over * {
 
 /* Textarea-based file editor */
 .file-editor-textarea {
+  flex: 1;
+  min-height: 0;
   width: 100%;
   min-width: 100%;
   height: 100%;