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

Styles/feed.css

@@ -25,6 +25,16 @@
 		display: none;
 	}
 
+	/* a custom emoji (CustomEmojis): the height of the text it sits in */
+	.custom-emoji {
+		display: inline;
+		height: 1.3em;
+		width: auto;
+		max-width: 3em;
+		vertical-align: -0.25em;
+		object-fit: contain;
+	}
+
 	.post-content .ellipsis::after {
 		content: "…";
 	}