Report-an-ad dialog: site dialog with no default reason (was a native prompt pre-filled with "broken")

Campaign #27 (house AdRevSplit text ad) was reported "broken" with no note while the target framed
and loaded fine; the report dialog was prompt() with 'broken' as the default value, so one stray OK
filed it. Now IAP.ask with an explicit, validated reason and an optional note; common.js tag bumped
on all pages.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

public/tx.html

@@ -34,7 +34,7 @@
     <p><a href="/ledger">← Back to the live ledger</a> · <a href="/contract">Read the contract review</a></p>
   </div>
 </section>
-<script src="/assets/common.js?v=20260914a"></script>
+<script src="/assets/common.js?v=20260916a"></script>
 <script src="/assets/tx.js?v=20260906m"></script>
 </body>
 </html>