Custom emoji, downvotes, blurhash and focal points on the cards

What other platforms send now shows as they meant it:
- custom emoji (a post's or account's :shortcode:) as their pictures in
  posts, names, content warnings, bios and fields: only the shortcodes the
  server listed, only http(s) pictures, never inside a tag, the shortcode
  kept as alt text;
- a threadiverse post's downvotes next to its favourites;
- blurhash placeholders until a picture loads (wwwroot/js/blurhash.js, a
  small decoder that watches the page), and a picture's focal point;
- an event's online link, participants and capacity, and whether it is
  tentative or cancelled.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LsXgEaXee4GCU1hwYgPJXw

wwwroot/index.html

@@ -28,6 +28,7 @@
 	<script>navigator.serviceWorker.register('service-worker.js');</script>
 	<script type="module" src="vendor/cally.js"></script>
 	<script src="main.js"></script>
+	<script src="js/blurhash.js"></script>
 </body>
 
 </html>