Switch file immediately on click, fire ITE in background (#353)

The file_edit inter-test event was recorded before the editor
switched, causing a noticeable delay on every filename click.
The UI switch does not depend on the server-assigned index, so
it is safe to run immediately while the POST fires in parallel.

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: JonJagger

source/app/views/kata/_filenames.erb

@@ -125,9 +125,8 @@ $(() => {
       $div.addClass('source');
     }
     $div.click(() => {
-      cd.saveAnyFileChangesITE(() => {
-        filenames.select(filename);
-      });
+      filenames.select(filename);
+      cd.saveAnyFileChangesITE(() => {});
     });
     return $div;
   };