feat(todo): dialogs on the desktop, the tabs reordered, a task's path and menu (ADR 0033, D11 to D14)

- halkyon_ui: showAdaptiveSheet shows a dialog on Linux, macOS and Windows
  at every width (bottom sheets stay on phones and tablets below expanded
  windows), so Learn and Train follow; SheetScaffold takes a heading in
  the title's place and may leave out its close button.
- Todo: the tabs are Inbox, Today, Upcoming, Browse, Today still opening;
  `serverpod start` launches the app on Linux, as it has no web build.
- A task's sheet shows where the task is (its project, an icon once tasks
  are above it, and the tasks above it, each opening what it names) and a
  ⋮ menu in place of its close button: when it was added (its UUID v7),
  Duplicate with its sub-tasks, hiding its done sub-tasks (synced in its
  payload), Close in the pane, Delete after asking. The description's icon
  stays by its first line.
- A row names its project and section at the end of its date's line; every
  menu entry has its icon.
- Learn: a studyset's path starts at the Library tab's icon, named by its
  tooltip.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Tizian 「ティツィアーン」 <raisondetredev@pm.me>

apps/todo/halkyon_todo_flutter/test/feature/task/task_payload_test.dart

@@ -45,6 +45,7 @@ void main() {
     reminders: const [30, 0],
     completedAt: DateTime(2026, 11, 2, 7),
     completions: [DateTime(2026, 10, 19, 7, 5), DateTime(2026, 10, 22, 6)],
+    hideDoneSubTasks: true,
   );
 
   group('a task', () {
@@ -84,6 +85,7 @@ void main() {
           DateTime(2026, 10, 19, 7, 5).toUtc().toIso8601String(),
           DateTime(2026, 10, 22, 6).toUtc().toIso8601String(),
         ],
+        'hideDoneSubTasks': true,
       });
       expect(
         written(encodeTask(const TaskContent(title: 'Milk', projectId: 'p'))),

apps/todo/halkyon_todo_flutter/test/feature/task/task_repository_test.dart

@@ -177,6 +177,45 @@ void main() {
     },
   );
 
+  test('duplicating a task copies it with its sub-tasks, theirs too, right '
+      'after it among its siblings', () async {
+    final tasks = await device(alice);
+    final first = await tasks.add(milk.copyWith(position: 1));
+    await tasks.add(milk.copyWith(title: 'Next', position: 2));
+    final sub = await tasks.add(
+      const TaskContent(
+        title: 'Oat',
+        projectId: 'inbox',
+        position: 1,
+      ).copyWith(parentId: () => first),
+    );
+    await tasks.add(
+      TaskContent(
+        title: 'Bottles',
+        projectId: 'inbox',
+        parentId: sub,
+        completedAt: DateTime(2026, 11, 2),
+      ),
+    );
+
+    final copy = await tasks.duplicate(first);
+
+    final all = {for (final t in await tasks.all()) t.id: t.content!};
+    expect(all, hasLength(7));
+    expect(all[copy]!.title, 'Buy milk');
+    expect(all[copy]!.position, 1.5, reason: 'between it and the next');
+    final copiedSub = all.entries.singleWhere(
+      (e) => e.value.parentId == copy,
+    );
+    expect(copiedSub.value.title, 'Oat');
+    expect(copiedSub.key, isNot(sub));
+    final copiedBottles = all.values.singleWhere(
+      (t) => t.parentId == copiedSub.key,
+    );
+    expect(copiedBottles.title, 'Bottles');
+    expect(copiedBottles.completed, isTrue, reason: 'copied as it was');
+  });
+
   test("deleting a project's or a section's tasks deletes only theirs, "
       'with their sub-tasks', () async {
     final phone = await device(alice);

apps/todo/halkyon_todo_flutter/test/feature/task/task_views_test.dart

@@ -106,4 +106,14 @@ void main() {
       ],
     );
   });
+
+  test('a task was added when its UUID v7 says, its first 48 bits the '
+      'milliseconds since 1970; another ID says nothing', () {
+    expect(
+      addedAt('019a3e2f-8c00-7000-8000-000000000000'),
+      DateTime.fromMillisecondsSinceEpoch(0x019a3e2f8c00),
+    );
+    expect(addedAt('not-an-id'), isNull);
+    expect(addedAt('019a3e2f-8c00-4000-8000-000000000000'), isNull);
+  });
 }