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/task/task_views_test.dart

@@ -116,4 +116,30 @@ void main() {
     expect(addedAt('not-an-id'), isNull);
     expect(addedAt('019a3e2f-8c00-4000-8000-000000000000'), isNull);
   });
+
+  test("Today's Plan (D30): overdue, today's without a time to plan, and "
+      "today's with a time, done ones left out; narrowed to the projects "
+      'picked, none picked keeping all', () {
+    final tasks = [
+      task('late', day: today.plus(-2), time: 9 * 60),
+      task('open', day: today, project: 'home'),
+      task('nine', day: today, time: 9 * 60),
+      task('eight', day: today, time: 8 * 60, project: 'home'),
+      task('done', day: today, time: 7 * 60, completed: true),
+      task('tomorrow', day: today.plus(1), time: 9 * 60),
+      task('undated'),
+    ];
+
+    final plan = planOf(tasks, today);
+    expect(plan.overdue.map((t) => t.id), ['late']);
+    expect(plan.toPlan.map((t) => t.id), ['open']);
+    expect(plan.timed.map((t) => t.id), ['eight', 'nine']);
+    expect(plan.count, 4);
+
+    final home = planOf(tasks, today, projectIds: {'home'});
+    expect(home.overdue, isEmpty);
+    expect(home.toPlan.map((t) => t.id), ['open']);
+    expect(home.timed.map((t) => t.id), ['eight']);
+    expect(home.count, 2);
+  });
 }