Player: now-playing title with cover, start banner, one status pill; media art for everyone

The swapper sends the media's poster and banner once (`art`, Jellyfin
images or AniList by parsed name); state carries their hashes and every
member fetches them from /i/ like avatars. state.media.swapBy names who
put the media up. uosc and the standard bar show cover, title and
episode; a banner card shows before playback starts. The top-left health
pill and the waiting pill become one frosted status pill in plain words.

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

apps/desktop/lib/src/session/now_playing.dart

@@ -0,0 +1,24 @@
+/// What the player shows about the current media: a title, an episode line
+/// and art. Art is by content hash (`state.media.art`), fetched by everyone
+/// (guests included) from the server they dialled; '' when there is none.
+class NowPlaying {
+  /// Series name for episodes, else the movie, file or link name.
+  final String title;
+  /// "S2 E4 · Episode title", "E12", or null (movies, links).
+  final String? episode;
+  /// Portrait cover (2:3) and wide banner; '' when none.
+  final String posterHash;
+  final String bannerHash;
+  const NowPlaying({required this.title, this.episode, this.posterHash = '', this.bannerHash = ''});
+
+  @override
+  bool operator ==(Object other) =>
+      other is NowPlaying &&
+      other.title == title &&
+      other.episode == episode &&
+      other.posterHash == posterHash &&
+      other.bannerHash == bannerHash;
+
+  @override
+  int get hashCode => Object.hash(title, episode, posterHash, bannerHash);
+}