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

CLAUDE.md

@@ -224,6 +224,11 @@ supplies:
   with its own `PublicAct`: joining an event (owner decision 2026-10-05) is asked once more, since the event's server
   shows who takes part. An event card shows the persona's participation (`privapub.event.participation`: pending,
   accepted, rejected) with Join or Leave, except for events by invitation or taken on another site (`join_mode`).
+- **What a card shows of other platforms:** custom emoji (`Helpers/CustomEmojis.cs`: a post's or account's `:shortcode:`
+  in its text, name, warning, bio and fields, as the picture the server listed, never inside a tag), a threadiverse
+  post's downvotes next to its favourites, blurhash placeholders until a picture loads (`wwwroot/js/blurhash.js`
+  watches the page for `img[data-blurhash]`), a picture's focal point (`object-position`), and an event's online
+  link, participants and status.
 - **Profiles and search** (`Pages/Profile.razor` at `/account/{id}`, `Pages/Search.razor` at `/search?q=`): a card's
   author and a notification's account open the profile in the app; "Open original" is the only way to the remote site.
   A card in a fixed-height flex column with `overflow-hidden` needs `flex-none`, or it collapses to nothing.