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>

apps/desktop/lib/src/jellyfin/accounts.dart

@@ -207,7 +207,7 @@ class JellyfinAccounts extends ChangeNotifier {
   /// Last failure text for an offline account.
   String? errorOf(String serverId) => _errors[serverId];
 
-  /// The Host tab's last Jellyfin pick, restored on the next start.
+  /// The last Jellyfin pick put up, restored in the Library on the next start.
   JellyfinMedia? get lastPick => _lastPick;
 
   /// Stable per install: Jellyfin keys devices and tokens by it.

apps/desktop/lib/src/jellyfin/accounts_panel.dart

@@ -74,7 +74,7 @@ class _JellyfinAccountsPanelState extends State<JellyfinAccountsPanel> {
                         Text('Jellyfin', style: t.titleMedium),
                         const SizedBox(height: 4),
                         const Text(
-                          'Browse your libraries in the Host tab and put up movies and episodes. '
+                          'Browse your libraries in the Library tab and put up movies and episodes. '
                           'Sign in with Quick Connect or your password; several servers are fine.',
                           style: TextStyle(color: Colors.grey),
                         ),

apps/desktop/lib/src/jellyfin/browser.dart

@@ -91,7 +91,7 @@ class _JellyfinBrowserState extends State<JellyfinBrowser> {
       const [HomeRoute()];
 
   /// Every navigation is saved per server (Hive), so the next browser
-  /// (Host tab, swap panel, next start) opens where this one was.
+  /// (the Library tab, next start) opens where this one was.
   void _remember() {
     final id = _account?.serverId;
     if (id != null) unawaited(_accounts.saveBrowseLocation(id, encodeBrowseStack(_stack)));