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>

test/builtin/default_layout/widget_test.dart

@@ -0,0 +1,52 @@
+import 'package:clide/builtin/default_layout/default_layout.dart';
+import 'package:clide/extension/extension.dart';
+import 'package:clide/kernel/kernel.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+import '../../helpers/kernel_fixture.dart';
+
+void main() {
+  group('DefaultLayoutExtension', () {
+    late KernelFixture f;
+
+    setUp(() async => f = await KernelFixture.create());
+    tearDown(() async => f.dispose());
+
+    test('activates and applies the classic preset', () async {
+      f.services.extensions.register(DefaultLayoutExtension());
+      await f.services.extensions.activateAll();
+      expect(
+          f.services.arrangement.positionOf(Slots.sidebar), SlotPosition.left);
+      expect(f.services.arrangement.sizeOf(Slots.sidebar), 240);
+      expect(f.services.arrangement.positionOf(Slots.workspace),
+          SlotPosition.center);
+      expect(f.services.arrangement.positionOf(Slots.statusbar),
+          SlotPosition.bottom);
+    });
+
+    test('contributes a layout.reset command', () async {
+      f.services.extensions.register(DefaultLayoutExtension());
+      await f.services.extensions.activateAll();
+      final reset = f.services.commands.get('layout.reset');
+      expect(reset, isNotNull);
+    });
+
+    test('layout.reset re-applies the preset', () async {
+      f.services.extensions.register(DefaultLayoutExtension());
+      await f.services.extensions.activateAll();
+      f.services.arrangement.setSize(Slots.sidebar, 300);
+      expect(f.services.arrangement.sizeOf(Slots.sidebar), 300);
+      final resp = await f.services.commands.execute('layout.reset');
+      expect(resp.ok, true);
+      expect(f.services.arrangement.sizeOf(Slots.sidebar), 240);
+    });
+
+    test('declares a layout preset contribution', () {
+      final ext = DefaultLayoutExtension();
+      expect(
+        ext.contributions.whereType<LayoutPresetContribution>(),
+        hasLength(1),
+      );
+    });
+  });
+}