feat(todo): quick add's keys, sub-projects' colours, a task's menu on a right click, and the completed tasks deleted at once

The developer's list of 9 Nov 2026, Todo's part:

- Quick add: the down arrow and Tab move into the description, with its
  cursor (halkyon_editor's fix); Escape closes the projects or labels
  suggested first, then closes quick add, what was typed discarded; the
  project's chip shows the project's colour.
- A project without a colour of its own shows its parent's, the nearest
  ancestor's with one (colorOfProject, TodoCubit.colorOf), wherever a
  project's colour shows; the project editor's "Same colour as its parent"
  keeps it so, and the parent picker shows each project in its colour. A
  project of its own always has one.
- The task pane's x closes it, always; Close left the ⋮ menu.
- A task's row opens its menu on a right click: Mark as done, Date, Move
  to, Labels, Priority, Deadline, Duplicate and Delete, the selection's
  actions for that one task.
- Delete completed tasks, in the ⋮ of the Inbox, Today, Upcoming and a
  project, with Undo: the tasks leave the list at once and are deleted
  once the snack bar goes without its Undo (halkyon_ui's showUndoSnackBar
  gains onKept).

Whats-New: Quick add: the arrow keys and Tab reach the description, and Escape closes it without saving.
Whats-New-De: Schnell hinzufügen: Pfeiltasten und Tab erreichen die Beschreibung, und Escape schließt es, ohne zu speichern.
Whats-New: Sub-projects take their parent's colour unless they have their own.
Whats-New-De: Unterprojekte übernehmen die Farbe ihres übergeordneten Projekts, wenn sie keine eigene haben.
Whats-New: A right click on a task opens its menu, with Move to and more; Delete completed tasks clears a list, with Undo.
Whats-New-De: Ein Rechtsklick auf eine Aufgabe öffnet ihr Menü, mit Verschieben nach und mehr; Erledigte Aufgaben löschen räumt eine Liste auf, mit Rückgängig.
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

@@ -892,6 +892,12 @@ abstract class AppLocalizations {
   /// **'\"{name}\" is deleted with its sections and tasks, on all your devices.'**
   String projectDeleteMessage(String name);
 
+  /// In a sub-project's editor: whether it shows in its parent's colour rather than one of its own (the developer's review, 9 Nov 2026).
+  ///
+  /// In en, this message translates to:
+  /// **'Same colour as its parent'**
+  String get projectInheritColor;
+
   /// A project's editor (ADR 0033, D28), as Todoist's Add project.
   ///
   /// In en, this message translates to:
@@ -1486,12 +1492,6 @@ abstract class AppLocalizations {
   /// **'Show done sub-tasks'**
   String get subTasksShowDone;
 
-  /// No description provided for @taskClose.
-  ///
-  /// In en, this message translates to:
-  /// **'Close'**
-  String get taskClose;
-
   /// No description provided for @taskPath.
   ///
   /// In en, this message translates to:
@@ -2517,6 +2517,18 @@ abstract class AppLocalizations {
   /// In en, this message translates to:
   /// **'You\'ve left {name}'**
   String locationLeft(String name);
+
+  /// A list's menu: deletes its done tasks, with an Undo (the developer's review, 9 Nov 2026).
+  ///
+  /// In en, this message translates to:
+  /// **'Delete completed tasks'**
+  String get tasksDeleteCompleted;
+
+  /// The snack bar after Delete completed tasks, with its Undo.
+  ///
+  /// In en, this message translates to:
+  /// **'{count, plural, =1{1 completed task deleted} other{{count} completed tasks deleted}}'**
+  String tasksCompletedDeleted(int count);
 }
 
 class _AppLocalizationsDelegate