Homepage: seamless theme music that keeps playing on /members/

Adds the eom.dev theme (Strudel) as a 16-bar Web Audio loop (Opus, AAC
fallback) with a Theme on/off button. Playback starts on the first
interaction unless the visitor turned it off. While it plays, links
between the homepage and membership pages are fetched and swapped in
place, so the music doesn't restart; sign-in, checkout, billing and
forms remain real navigations.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

htdocs/index.html

@@ -323,6 +323,7 @@
 </main>
 <script type="module" src="/static/peertube-feeds.mjs"></script>
 <script type="module" src="/static/gitea-projects.mjs"></script>
+<script type="module" src="/static/theme-player.mjs"></script>
 <!--#include virtual="/common/footer.html" -->
 </body>
 </html>