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/lib/l10n/app_de.arb

@@ -257,5 +257,18 @@
   "monthMore": "{count} weitere",
   "dayHeadingPattern": "EEEE, d. MMM",
   "overdueHide": "Überfälliges ausblenden",
-  "overdueShow": "Überfälliges einblenden"
+  "overdueShow": "Überfälliges einblenden",
+  "planButton": "Plan: {count}",
+  "planTitle": "Plan",
+  "planShow": "Plan einblenden",
+  "planHide": "Plan ausblenden",
+  "planToPlan": "Zu planen",
+  "planTimeBlocked": "Eingeplant",
+  "planEmpty": "Nichts zu planen",
+  "planDropHint": "Hier ablegen, um die Uhrzeit zu entfernen",
+  "planGroupHide": "{group} ausblenden",
+  "planGroupShow": "{group} einblenden",
+  "planAllProjects": "Alle Projekte",
+  "planProjectsCount": "{count, plural, =1{1 Projekt} other{{count} Projekte}}",
+  "planFilterTitle": "Nach Projekt filtern"
 }