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/settings_tab.dart

@@ -0,0 +1,170 @@
+import 'package:flutter/material.dart';
+import 'package:signals/signals_flutter.dart';
+
+import '../jellyfin/accounts.dart';
+import '../jellyfin/accounts_panel.dart';
+import '../screens/home/about_page.dart';
+import '../screens/home/settings_page.dart';
+import '../update/update_controller.dart';
+import 'avatar.dart';
+import 'motion.dart';
+
+/// The Settings tab's pages, in nav order.
+enum SettingsSection {
+  profile(Icons.person_outline, 'Profile'),
+  player(Icons.play_circle_outline, 'Player'),
+  integrations(Icons.extension_outlined, 'Jellyfin & integrations'),
+  updates(Icons.system_update_alt, 'Updates'),
+  shortcuts(Icons.keyboard_outlined, 'Keyboard shortcuts'),
+  about(Icons.info_outline, 'About');
+
+  final IconData icon;
+  final String label;
+  const SettingsSection(this.icon, this.label);
+}
+
+/// App-wide settings under a left nav (chips on top when narrow). The
+/// pages hold the existing settings panels; the shell owns [section] so
+/// the profile card can open a page.
+class SettingsTab extends StatelessWidget {
+  final SettingsSection section;
+  final ValueChanged<SettingsSection> onSection;
+  final VoidCallback? onEditProfile;
+  final UpdateController? updates;
+  /// Defaults to [JellyfinAccounts.instance].
+  final JellyfinAccounts? jellyfin;
+  const SettingsTab({
+    super.key,
+    required this.section,
+    required this.onSection,
+    this.onEditProfile,
+    this.updates,
+    this.jellyfin,
+  });
+
+  List<Widget> _page(BuildContext context) {
+    switch (section) {
+      case SettingsSection.profile:
+        return [
+          SettingsPanel(
+            title: 'You',
+            child: SignalBuilder(
+              builder: (context) {
+                final me = selfAvatarInfo();
+                return ListTile(
+                  contentPadding: EdgeInsets.zero,
+                  leading: StatusAvatar(info: me, size: 48, badges: false, ring: false),
+                  title: Text(me.name == '?' ? 'No name yet' : me.name),
+                  subtitle: const Text('Name, picture and colour: click your avatar in the top left'),
+                  trailing: onEditProfile == null
+                      ? null
+                      : TextButton(onPressed: onEditProfile, child: const Text('Edit')),
+                );
+              },
+            ),
+          ),
+        ];
+      case SettingsSection.player:
+        return const [
+          SettingsPanel(
+            title: 'Player',
+            child: Column(
+              crossAxisAlignment: CrossAxisAlignment.stretch,
+              children: [HwdecSetting(), SizedBox(height: 12), MpvControlsSetting()],
+            ),
+          ),
+          SettingsPanel(title: 'Video quality & shaders', child: ShaderSettings()),
+        ];
+      case SettingsSection.integrations:
+        return [
+          Padding(
+            padding: const EdgeInsets.only(bottom: 16),
+            child: JellyfinAccountsPanel(accounts: jellyfin ?? JellyfinAccounts.instance),
+          ),
+          const SettingsPanel(title: 'Jellyfin playback', child: AutoAdvanceSetting()),
+        ];
+      case SettingsSection.updates:
+        return [SettingsPanel(title: 'Updates', child: UpdateSettings(controller: updates))];
+      case SettingsSection.shortcuts:
+        return const [SettingsPanel(title: 'Keyboard shortcuts', child: ShortcutList())];
+      case SettingsSection.about:
+        return [AboutPanel(updates: updates)];
+    }
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    return LayoutBuilder(
+      builder: (context, box) {
+        final narrow = box.maxWidth < 760;
+        final nav = narrow
+            ? SizedBox(
+                height: 52,
+                child: HScroll(
+                  builder: (c) => ListView(
+                    controller: c,
+                    scrollDirection: Axis.horizontal,
+                    padding: const EdgeInsets.fromLTRB(20, 8, 20, 4),
+                    children: [
+                      for (final s in SettingsSection.values)
+                        Padding(
+                          padding: const EdgeInsets.only(right: 8),
+                          child: ChoiceChip(
+                            key: ValueKey('settings-${s.name}'),
+                            label: Text(s.label),
+                            selected: section == s,
+                            onSelected: (_) => onSection(s),
+                          ),
+                        ),
+                    ],
+                  ),
+                ),
+              )
+            : SizedBox(
+                width: 250,
+                child: ListView(
+                  padding: const EdgeInsets.fromLTRB(16, 20, 8, 20),
+                  children: [
+                    for (final s in SettingsSection.values)
+                      ListTile(
+                        key: ValueKey('settings-${s.name}'),
+                        selected: section == s,
+                        shape: RoundedRectangleBorder(borderRadius: BorderRadius.circular(12)),
+                        leading: Icon(s.icon, size: 20),
+                        title: Text(s.label),
+                        onTap: () => onSection(s),
+                      ),
+                  ],
+                ),
+              );
+        final page = fadeThrough(
+          KeyedSubtree(
+            key: ValueKey(section),
+            child: ListView(
+              padding: const EdgeInsets.fromLTRB(20, 20, 24, 24),
+              children: [
+                Align(
+                  alignment: Alignment.topLeft,
+                  child: ConstrainedBox(
+                    constraints: const BoxConstraints(maxWidth: 760),
+                    child: Column(
+                      crossAxisAlignment: CrossAxisAlignment.stretch,
+                      children: [
+                        Text(section.label, style: Theme.of(context).textTheme.headlineSmall),
+                        const SizedBox(height: 14),
+                        ..._page(context),
+                      ],
+                    ),
+                  ),
+                ),
+              ],
+            ),
+          ),
+        );
+        return narrow
+            ? Column(children: [nav, Expanded(child: page)])
+            : Row(children: [nav, Expanded(child: page)]);
+      },
+    );
+  }
+}