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/os.dart

@@ -0,0 +1,72 @@
+import 'dart:async';
+import 'dart:io';
+
+import 'package:clide/kernel/src/events/bus.dart';
+import 'package:clide/kernel/src/events/types.dart';
+import 'package:clide/kernel/src/log.dart';
+import 'package:flutter/foundation.dart';
+
+class OsLifecycleEvent extends ClideEvent {
+  const OsLifecycleEvent(this._kind);
+  final String _kind;
+  @override
+  String get subsystem => 'os';
+  @override
+  String get kind => _kind;
+}
+
+class OsBridge {
+  OsBridge({required Logger log, required EventBus events})
+      : _log = log,
+        _events = events;
+
+  final Logger _log;
+  final EventBus _events;
+
+  Future<bool> openURL(String url) async {
+    final cmd = _openCommand();
+    if (cmd == null) {
+      _log.warn('os', 'openURL unsupported on ${Platform.operatingSystem}');
+      return false;
+    }
+    try {
+      final r = await Process.run(cmd[0], [...cmd.skip(1), url]);
+      return r.exitCode == 0;
+    } catch (e) {
+      _log.warn('os', 'openURL failed', error: e);
+      return false;
+    }
+  }
+
+  Future<bool> reveal(String path) async {
+    final cmd = _revealCommand(path);
+    if (cmd == null) return false;
+    try {
+      final r = await Process.run(cmd[0], cmd.skip(1).toList());
+      return r.exitCode == 0;
+    } catch (e) {
+      _log.warn('os', 'reveal failed', error: e);
+      return false;
+    }
+  }
+
+  /// Fire an OS lifecycle event (called by the platform wiring).
+  @visibleForTesting
+  void fire(String kind) {
+    _events.emit(OsLifecycleEvent(kind));
+  }
+
+  static List<String>? _openCommand() {
+    if (Platform.isLinux) return ['xdg-open'];
+    if (Platform.isMacOS) return ['open'];
+    if (Platform.isWindows) return ['cmd', '/c', 'start', ''];
+    return null;
+  }
+
+  static List<String>? _revealCommand(String path) {
+    if (Platform.isLinux) return ['xdg-open', File(path).parent.path];
+    if (Platform.isMacOS) return ['open', '-R', path];
+    if (Platform.isWindows) return ['explorer', '/select,', path];
+    return null;
+  }
+}