feat(todo): a task's title field hints "Task name", as Todoist's

The title's placeholder in quick add and in a task's sheet read "What's
to be done?"; the developer asked for Todoist's plainer "Task name"
("Aufgabenname").

Whats-New: A task's title field now says "Task name".
Whats-New-De: Das Titelfeld einer Aufgabe zeigt jetzt „Aufgabenname“.

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/app/todo_app_test.dart

@@ -1280,6 +1280,14 @@ void main() {
           reason: 'the list in view',
         );
         expect(find.text('Add task'), findsNothing, reason: 'no title bar');
+        expect(
+          find.descendant(
+            of: find.byType(QuickAddBar),
+            matching: find.text('Task name'),
+          ),
+          findsOneWidget,
+          reason: "its hint, as Todoist's (the developer's review, 4 Nov 2026)",
+        );
       });
 
       testWidgets('typed tokens set the task, shown on its chips, a label '