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/test/feature/task/task_views_test.dart

@@ -174,4 +174,46 @@ void main() {
       ['other'],
     );
   });
+
+  group('Given done and open tasks (Delete completed tasks; the '
+      "developer's review, 9 Nov 2026),", () {
+    final tasks = [
+      task('open'),
+      task('done', completed: true),
+      task('done sub', parent: 'open', completed: true),
+      task('done elsewhere', project: 'work', completed: true),
+      task('done today', project: 'work', day: today, completed: true),
+      task('done yesterday', day: today.plus(-1), completed: true),
+      task('done next week', day: today.plus(7), completed: true),
+      task('open today', day: today),
+    ];
+    List<String> ids(List<OpenTask> found) => [
+      for (final task in found) task.id,
+    ];
+
+    test("then a project's are its done tasks, sub-tasks too.", () {
+      expect(
+        ids(completedIn(tasks, projectId: 'inbox')),
+        unorderedEquals([
+          'done',
+          'done sub',
+          'done yesterday',
+          'done next week',
+        ]),
+      );
+    });
+
+    test("then Today's are the done tasks dated today.", () {
+      expect(ids(completedIn(tasks, from: today, until: today)), [
+        'done today',
+      ]);
+    });
+
+    test("then Upcoming's are the done tasks dated from today on.", () {
+      expect(
+        ids(completedIn(tasks, from: today)),
+        unorderedEquals(['done today', 'done next week']),
+      );
+    });
+  });
 }