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_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.