feat(todo): Upcoming's tasks dragged onto another day (ADR 0033, D16)

A row of Upcoming, overdue ones too, held and dropped on another day
moves there, its time, duration and recurrence kept; Moved to … offers
Undo. The tint over a day a drag hovers is laid beside the rows, not
around them, which paint on the Material beneath.

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

@@ -1107,6 +1107,12 @@ abstract class AppLocalizations {
   /// In en, this message translates to:
   /// **'Drop here to cancel'**
   String get addTaskCancel;
+
+  /// Snack bar after a task was dragged onto another day in Upcoming (ADR 0033, D16).
+  ///
+  /// In en, this message translates to:
+  /// **'Moved to {day}'**
+  String taskMovedTo(String day);
 }
 
 class _AppLocalizationsDelegate