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>

packages/halkyon_ui/test/widget/adaptive_sheet_test.dart

@@ -48,7 +48,8 @@ void main() {
     await tester.pumpAndSettle();
   }
 
-  testWidgets('is a bottom sheet below expanded windows', (tester) async {
+  testWidgets('is a bottom sheet below expanded windows on a phone or a '
+      'tablet', (tester) async {
     await open(tester, width: 839);
 
     expect(find.byType(BottomSheet), findsOneWidget);
@@ -62,6 +63,23 @@ void main() {
     expect(find.byType(BottomSheet), findsNothing);
   });
 
+  for (final platform in [
+    TargetPlatform.linux,
+    TargetPlatform.macOS,
+    TargetPlatform.windows,
+  ]) {
+    testWidgets('is a dialog on the desktop however narrow the window '
+        '(${platform.name})', (tester) async {
+      debugDefaultTargetPlatformOverride = platform;
+      addTearDown(() => debugDefaultTargetPlatformOverride = null);
+      await open(tester, width: 400);
+
+      expect(find.byType(Dialog), findsOneWidget);
+      expect(find.byType(BottomSheet), findsNothing);
+      debugDefaultTargetPlatformOverride = null;
+    });
+  }
+
   for (final width in [400.0, 1200.0]) {
     testWidgets('keeps its close button and footer in view above a long body '
         '(${width.round()} wide)', (tester) async {
@@ -184,6 +202,43 @@ void main() {
     });
   });
 
+  testWidgets("a heading of its own takes the title's place, and the close "
+      'button may give way to its action', (tester) async {
+    tester.view.physicalSize = const Size(400, 900);
+    tester.view.devicePixelRatio = 1;
+    addTearDown(tester.view.reset);
+    await tester.pumpWidget(
+      MaterialApp(
+        localizationsDelegates: HalkyonUiLocalizations.localizationsDelegates,
+        supportedLocales: HalkyonUiLocalizations.supportedLocales,
+        home: Scaffold(
+          body: Builder(
+            builder: (context) => TextButton(
+              onPressed: () => showAdaptiveSheet<void>(
+                context,
+                builder: (context) => const SheetScaffold(
+                  title: 'Task',
+                  heading: Text('Inbox › Shopping'),
+                  closeButton: false,
+                  action: Text('More'),
+                  body: Text('Body'),
+                ),
+              ),
+              child: const Text('Open'),
+            ),
+          ),
+        ),
+      ),
+    );
+    await tester.tap(find.text('Open'));
+    await tester.pumpAndSettle();
+
+    expect(find.text('Inbox › Shopping'), findsOneWidget);
+    expect(find.text('Task'), findsNothing);
+    expect(find.byTooltip('Close'), findsNothing);
+    expect(find.text('More'), findsOneWidget);
+  });
+
   testWidgets('a body that fits shows no lines', (tester) async {
     await open(tester, width: 400);