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/learn/halkyon_learn_flutter/test/feature/studyset/widget/studyset_screen_test.dart

@@ -321,7 +321,22 @@ void main() {
       of: find.byType(StudysetBreadcrumb),
       matching: find.text(text),
     );
-    expect(step('Library'), findsOneWidget);
+    // The library is its icon, named by its tooltip (Todo's ADR 0033).
+    expect(step('Library'), findsNothing);
+    expect(
+      find.descendant(
+        of: find.byType(StudysetBreadcrumb),
+        matching: find.byTooltip('Library'),
+      ),
+      findsOneWidget,
+    );
+    expect(
+      find.descendant(
+        of: find.byType(StudysetBreadcrumb),
+        matching: find.byIcon(LucideIcons.book),
+      ),
+      findsOneWidget,
+    );
     expect(step('Japanese'), findsOneWidget);
     expect(step('Kana'), findsOneWidget);
     expect(step('›'), findsNWidgets(2));
@@ -1412,7 +1427,7 @@ void main() {
             .getCenter(
               find.descendant(
                 of: find.byType(StudysetBreadcrumb),
-                matching: find.text('Library'),
+                matching: find.byIcon(LucideIcons.book),
               ),
             )
             .dy,
@@ -1576,7 +1591,9 @@ void main() {
             .ancestor(
               of: find.descendant(
                 of: find.byType(StudysetBreadcrumb),
-                matching: find.text(text),
+                matching: text == 'Library'
+                    ? find.byIcon(LucideIcons.book)
+                    : find.text(text),
               ),
               matching: find.byType(GestureDetector),
             )