Address review: restore shields.io widgets and remove test script

Restore the dashboard and Discourse Forums shields.io badge widgets
in the header navbar — they are still functional. Also remove
test_cleanup.sh as tests are not needed for website cleanup.

Requested by @lefticus in PR #5 review.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: leftibot

_includes/header.html

@@ -61,6 +61,12 @@
       <li>
         <a href="http://codecov.io/github/ChaiScript/ChaiScript?branch=master"><img src="http://codecov.io/github/ChaiScript/ChaiScript/coverage.svg?branch=master" alt="Coverage Status" /></a>
       </li>
+      <li>
+        <a href="http://chaiscript.com/ChaiScript-BuildResults/index.html"><img src="https://img.shields.io/badge/dashboard-online-green.svg"/></a>
+      </li>
+      <li>
+        <a href="http://discourse.chaiscript.com"><img src="https://img.shields.io/badge/Discourse_Forums--green.svg"/></a>
+      </li>
     </ul>
   </div>
 </div>