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/shell/library_tab.dart

@@ -0,0 +1,79 @@
+import 'package:flutter/material.dart';
+import 'package:sync_relay_core/core.dart' show HelloMedia;
+
+import '../jellyfin/accounts.dart';
+import '../jellyfin/browse_scope.dart' show BrowseStart;
+import '../jellyfin/session_media.dart';
+import '../screens/home/media_picker.dart';
+import '../screens/session/swap_panel.dart';
+
+/// What putting up a Jellyfin pick sends: its ref (no URL, no token).
+/// Throws [FormatException] with a user-facing message when the server is
+/// not linked any more or its sign-in expired.
+HelloMedia putUpJellyfinMedia(JellyfinAccounts accounts, JellyfinMedia media) {
+  if (accounts.account(media.serverId) == null) {
+    throw const FormatException('that Jellyfin server is not linked any more — pick again');
+  }
+  if (accounts.statusOf(media.serverId) == JellyfinAccountStatus.expired) {
+    throw const FormatException('Jellyfin sign-in expired — reconnect it in Settings → Jellyfin & integrations');
+  }
+  return mediaForPick(media);
+}
+
+/// Brings back the last Jellyfin pick (kept in the Jellyfin box) once the
+/// accounts are read, unless something else was picked meanwhile or
+/// [alive] says the picker is gone.
+Future<void> restoreLastPick(
+    MediaPickerController c, JellyfinAccounts accounts, bool Function() alive) async {
+  final hadMedia = c.selection != null;
+  try {
+    await accounts.ensureLoaded();
+  } catch (_) {
+    return;
+  }
+  final pick = accounts.lastPick;
+  if (!alive() || pick == null || c.jellyfin != null) return;
+  if (accounts.account(pick.serverId) == null) return;
+  final source = c.source;
+  c.pickJellyfin(pick);
+  if (hadMedia) c.source = source;
+}
+
+/// Library (round 1): the media picker as the "put it up" view. Offline
+/// it browses, with a hint that watching needs a server.
+class LibraryTab extends StatelessWidget {
+  final MediaPickerController controller;
+  final JellyfinAccounts accounts;
+  final bool online;
+  final bool isHost;
+  final BrowseStart? jellyfinStart;
+  /// Puts the pick up; returns an error text, or null when sent.
+  final Future<String?> Function(PickedMedia media) onPutUp;
+  final VoidCallback? onPutUpDone;
+  final VoidCallback? onOpenIntegrations;
+  const LibraryTab({
+    super.key,
+    required this.controller,
+    required this.accounts,
+    required this.online,
+    required this.isHost,
+    required this.onPutUp,
+    this.onPutUpDone,
+    this.jellyfinStart,
+    this.onOpenIntegrations,
+  });
+
+  @override
+  Widget build(BuildContext context) {
+    return SwapPanel(
+      controller: controller,
+      accounts: accounts,
+      isHost: isHost,
+      jellyfinStart: jellyfinStart,
+      onSwap: onPutUp,
+      onDone: onPutUpDone,
+      onOpenIntegrations: onOpenIntegrations,
+      disabledHint: online ? null : 'Join or host to watch together',
+    );
+  }
+}