feat(todo): Today laid out as a calendar, planned from its Plan by dragging, as Todoist's desktop Today (ADR 0033, D30)

The developer asked for Todoist's desktop Today planning: a day of hours
and a Plan beside it, tasks dragged from it onto an hour. Today gets a
Display, its layout alone (List or Calendar), kept in the person's sealed
settings row as Upcoming's (`TodayView`, the payload's `today`, schema
still 1). Its Calendar is one day of `HourGrid`; *Plan: n* in its app bar
shows or hides the Plan (`PlanPanel`): Overdue with Reschedule, To plan
(today's without a time) and Time-blocked (today's with one), each
folding with its count, narrowed for the session by *All projects*'
Filter by project (a search and a box a project, a sub-project with its
parents' path). A row dropped on an hour is moved to today at that time,
its duration kept; a block dropped on the Plan loses its time; both undone
from the snack bar, through `moveTask`. From a medium width of Today's own
on the Plan stands beside the day, shown or hidden as remembered; on a
phone it is a sheet over the day's foot (the developer's choice, over the
Plan on wide windows alone and over a strip above the day), part of the
screen rather than a modal route, so that the day behind it takes the
drop, and it lowers to its heading while one of its rows is held.

Whats-New: Today's Display offers a Calendar layout: today's hours, with a Plan of what is overdue, to plan and time-blocked, whose tasks you drag onto an hour.
Whats-New-De: Die Anzeige von Heute bietet das Layout Kalender: die Stunden des Tages, mit einem Plan aus Überfälligem, Zu planen und Eingeplant, dessen Aufgaben du auf eine Stunde ziehst.

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/settings/settings_payload_test.dart

@@ -69,6 +69,25 @@ void main() {
     expect(decodeSettings(payload({'schemaVersion': 2})), isNull);
   });
 
+  test("Today's Display and whether its Plan stands beside the day read "
+      'back as they were set (D30); an unknown layout as at first', () {
+    const settings = TodoSettings(
+      today: TodayView(layout: TodayLayout.calendar, plan: false),
+    );
+    expect(decodeSettings(encodeSettings(settings)), settings);
+    expect(written(settings)['today'], {'layout': 'calendar', 'plan': false});
+    expect(const TodoSettings().today.plan, isTrue, reason: 'open at first');
+    expect(
+      decodeSettings(
+        payload({
+          'schemaVersion': 1,
+          'today': {'layout': 'board'},
+        }),
+      ),
+      const TodoSettings(),
+    );
+  });
+
   test("D4's settings of tasks and reminders read back as they were set", () {
     const settings = TodoSettings(
       tasks: TaskSettings(weekStart: DateTime.sunday, resetSubTasks: false),