1.0 shell: one window with a party strip; protocol 9 profile + avatars by hash

The shell (lib/src/shell/) replaces the Home and session screens:
- Party strip: profile, Library / Schedule / Settings tabs, Join and
  Host cards (hosting no longer takes media), status-ring avatar stack
  with the member list, chat & activity panel, Leave.
- The real session player is mounted once and shown full, as a
  draggable corner-snapping mini player, or fullscreen (window_manager,
  party and toasts overlaid); the Video is never mounted twice.
- Profile popover with inline rename, colour and a crop picker (256 px
  PNG), pushed live to the session; avatar toasts; waiting pill.
- Motion kit (fastEaseInToSlowEaseOut, fade-through, popovers,
  mouse-drag/wheel horizontal scrolling).
- Library = the existing picker for now (restyled next round); Schedule
  = the new SchedulePage; Settings = left nav over the existing panels.

Protocol 9 (packages/core, packages/server, sync client):
- {"t":"profile"} renames / changes the picture mid-session ("rename",
  "avatar" feed actions); names are cleaned the same way at hello.
- state.members carry avatarHash; pictures are served once from
  /a/<sid>/<token>/<hash> (PNG/JPEG/WebP/GIF by magic bytes only) and
  cached by hash in the app (AvatarCache).

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

packages/server/lib/src/session.dart

@@ -7,15 +7,15 @@ enum MediaGate { ok, gone, unauthorized, forbidden, offline }
 
 class ViewerToken {
   final String token;
-  final String name;
-  final String avatar;
+  /// Cleaned ([cleanMemberName]); follows `profile` renames.
+  String name;
   bool kicked = false;
   /// Sent the server's host key in hello: the hosting app's own client.
   bool isHost = false;
   int bytesServed = 0;
   DateTime lastSeen;
   Future<void> Function(String reason)? onKick;
-  ViewerToken({required this.token, required this.name, this.avatar = ''})
+  ViewerToken({required this.token, required this.name})
       : lastSeen = DateTime.now().toUtc();
 
   bool isStale(Duration timeout, [DateTime? now]) =>
@@ -53,18 +53,14 @@ class Session {
 
   Session({required this.id, required this.secret});
 
+  /// The avatar is only checked here; the engine keeps the picture.
   String issueToken(String name, String avatar) {
     if (avatar.length > RelayConstants.maxAvatarBytes) {
       throw const AuthException('avatar too large');
     }
-    final trimmed = name.trim();
-    final cleanName = trimmed.isEmpty
-        ? '?'
-        : trimmed.substring(
-            0, trimmed.length.clamp(0, RelayConstants.maxNameLength));
     final bytes = List<int>.generate(16, (_) => _random.nextInt(256));
     final token = bytes.map((b) => b.toRadixString(16).padLeft(2, '0')).join();
-    tokens[token] = ViewerToken(token: token, name: cleanName, avatar: avatar);
+    tokens[token] = ViewerToken(token: token, name: cleanMemberName(name));
     return token;
   }