The file manager spec cleans its directory before it fills it

One run out of a dozen failed on "creates a folder and returns to the
directory": the spec created its artifact directory under `tmp/` and only
removed it afterwards, so anything left behind by an interrupted run was still
there when the next one started, and `mkdir` on an existing folder answers with
the alert instead of the notice.

It removes the directory first now. The suite is green across ten consecutive
runs and every seed tried, including the one that failed.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

apps/api/spec/requests/admin_files_spec.rb

@@ -8,6 +8,7 @@ RSpec.describe "Admin file manager", type: :request do
   let(:container) { Rails.root.join("tmp/files-spec").to_s }
 
   before do
+    FileUtils.rm_rf(container)
     FileUtils.mkdir_p(File.join(container, "mygame-1.0"))
     File.write(File.join(container, "mygame-1.0.zip"), "zipdata")
     allow(WarpEngine.config).to receive(:file_container_path).and_return(container)