Add ReportMailer preview for devs

spec/mailers/previews/report_mailer_preview.rb

@@ -0,0 +1,10 @@
+# frozen_string_literal: true
+
+# Preview all emails at http://localhost:3000/rails/mailers/report_mailer
+class ReportMailerPreview < ActionMailer::Preview
+  def report_ready
+    ReportMailer.with(
+      blob: ReportBlob.last,
+    ).report_ready
+  end
+end