Add to Calendar: hand phones the .ics file instead of a Google link

On a phone the Google Calendar app claims calendar.google.com links and opens
its own home screen, dropping the event. The pop-up now offers one "Add to
Calendar" button that goes to the calendar file on iOS/Android (served inline
so the phone hands it to its calendar) and to the Google event editor on
desktop, with the other route as the second button either way. The .ics is
also folded to RFC 5545 line lengths so Outlook accepts it.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

public/app.html

@@ -28,5 +28,5 @@
     <a class="btn btn-primary" href="/my">Open the dashboard</a>
   </div>
 </main>
-<script src="/app.js"></script>  <script src="/announce.js?v=20260916a"></script>
+<script src="/app.js"></script>  <script src="/announce.js?v=20260922a"></script>
 </body></html>