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/lib/l10n/app_de.arb

@@ -81,7 +81,7 @@
   "taskAddTitle": "Aufgabe hinzufügen",
   "taskAdd": "Hinzufügen",
   "taskAddOn": "Aufgabe für {day} hinzufügen",
-  "taskTitleHint": "Was ist zu tun?",
+  "taskTitleHint": "Aufgabenname",
   "taskDescription": "Beschreibung",
   "taskDescriptionHint": "Beschreibung",
   "taskComplete": "Als erledigt markieren",

apps/todo/halkyon_todo_flutter/lib/l10n/app_en.arb

@@ -181,7 +181,7 @@
       }
     }
   },
-  "taskTitleHint": "What's to be done?",
+  "taskTitleHint": "Task name",
   "taskDescription": "Description",
   "taskDescriptionHint": "Description",
   "taskComplete": "Mark as done",

apps/todo/halkyon_todo_flutter/lib/l10n/app_localizations.dart

@@ -589,7 +589,7 @@ abstract class AppLocalizations {
   /// No description provided for @taskTitleHint.
   ///
   /// In en, this message translates to:
-  /// **'What\'s to be done?'**
+  /// **'Task name'**
   String get taskTitleHint;
 
   /// No description provided for @taskDescription.

apps/todo/halkyon_todo_flutter/lib/l10n/app_localizations_de.dart

@@ -291,7 +291,7 @@ class AppLocalizationsDe extends AppLocalizations {
   }
 
   @override
-  String get taskTitleHint => 'Was ist zu tun?';
+  String get taskTitleHint => 'Aufgabenname';
 
   @override
   String get taskDescription => 'Beschreibung';

apps/todo/halkyon_todo_flutter/lib/l10n/app_localizations_en.dart

@@ -291,7 +291,7 @@ class AppLocalizationsEn extends AppLocalizations {
   }
 
   @override
-  String get taskTitleHint => 'What\'s to be done?';
+  String get taskTitleHint => 'Task name';
 
   @override
   String get taskDescription => 'Description';

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 '