dissolve app/ into repo root (D-056)

Single Flutter package at the repo root. All code, tests, assets,
and platform directories moved from app/ to root. Package renamed
from clide_app to clide — all imports rewritten. Merged pubspec
combines core (ffi) and app (flutter, yaml, xterm) dependencies.
Makefile simplified: no APP_PRESENT conditionals, no cd, no daemon
lifecycle. 317 tests pass.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

lib/kernel/src/tray.dart

@@ -0,0 +1,27 @@
+import 'package:clide/extension/src/contribution.dart';
+import 'package:flutter/foundation.dart';
+
+/// Tier-0 stub for OS tray / menu-bar integration.
+///
+/// Flutter desktop tray requires platform-channel wiring; this registry
+/// holds the contributions so extensions can declare them today. Real
+/// OS integration lands with a small per-platform channel in a later
+/// tier.
+class TrayRegistry extends ChangeNotifier {
+  final Map<String, TrayItemContribution> _items = {};
+
+  void add(TrayItemContribution item) {
+    _items[item.id] = item;
+    notifyListeners();
+  }
+
+  void remove(String id) {
+    if (_items.remove(id) != null) notifyListeners();
+  }
+
+  Iterable<TrayItemContribution> get items {
+    final sorted = _items.values.toList()
+      ..sort((a, b) => a.priority.compareTo(b.priority));
+    return sorted;
+  }
+}