Restructure step 2: Status as one computed level, the Notifier's real policy, system notifications

- Status: computed from connection, presence, hold, relay, player facts;
  no setters (health writes and HealthStatus gone); pill, strip and
  source line read it; transitions go to the Notifier.
- Notifier: noticeFor(event, context) with self presence, alone, window
  activity, playing and prefs; toasts for joins/leaves/returns/swaps/
  Up next adds (with picture)/problems/chat, the rest logged; while
  sitting out only chat, nudges, starting, Up next (+ joins if chosen);
  alone no social notices; replayed lines logged; owns its toast timer.
- System notifications (flutter_local_notifications: D-Bus on Linux,
  WinRT on Windows) when the window isn't focused; a click focuses it.
- Toasts sit above the control bar and move with it.
- Versions: each member's in the members card and avatar tooltip,
  the server's in the card header; the strip no longer shows it.

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

apps/desktop/lib/src/shell/avatar.dart

@@ -30,6 +30,8 @@ class AvatarInfo {
   /// How it gets the media and its buffer ([MemberDelivery.detail]), for
   /// the hover; empty when unknown.
   final String delivery;
+  /// Their Starsync version (`members[].app`), for the hover; '' unknown.
+  final String app;
   const AvatarInfo({
     this.id = '',
     required this.name,
@@ -44,6 +46,7 @@ class AvatarInfo {
     this.self = false,
     this.error = '',
     this.delivery = '',
+    this.app = '',
   });
 
   /// Sitting out.
@@ -136,6 +139,7 @@ AvatarInfo memberAvatarInfo(MemberView m, StateBroadcast? r, SessionCoordinator
     self: self,
     error: m.error,
     delivery: delivery == null ? '' : memberDeliveryOf(m, r!, delivery).detail,
+    app: m.app,
   );
 }
 
@@ -332,6 +336,7 @@ class _AvatarStackState extends State<AvatarStack> {
                           ? visible[i].name
                           : "${visible[i].name} can't play this: ${visible[i].error}",
                       if (visible[i].delivery.isNotEmpty) visible[i].delivery,
+                      if (visible[i].app.isNotEmpty) 'Starsync ${visible[i].app}',
                     ].join('\n'),
                     child: StatusAvatar(info: visible[i], size: size),
                   ),