Fix rubocop Lint/UselessAssignment for rescue variable

The `=> e` capture is unused after changing `raise e` to bare `raise`.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: AbanoubGhadban

react_on_rails_pro/app/helpers/react_on_rails_pro_helper.rb

@@ -438,7 +438,7 @@ def consumer_stream_async(on_complete:)
       stream = yield
       process_stream_chunks(stream, first_chunk_var, all_chunks)
       on_complete&.call(all_chunks)
-    rescue StandardError => e
+    rescue StandardError
       # Resolve first_chunk_var if not yet resolved, to prevent caller from hanging
       begin
         first_chunk_var.value = nil