feat(todo): side panes widen by their line, and a tap adds a task (ADR 0033, D33)

The line beside the task pane and Today's Plan is dragged, between 300 px
for the pane and 360 px beside it, each pane's width kept on the device.
A tap or click in the hour grid opens quick add at the quarter hour under
it, on a phone too, as where it lands says when; a long press takes
quarter hours as well. A tap that stops the day scrolling adds nothing.

Whats-New: Drag the line beside a task or the Plan to resize it; tap or click into the calendar to add a task at that time.
Whats-New-De: Ziehe die Linie neben einer Aufgabe oder dem Plan, um die Breite zu ändern; tippe oder klicke in den Kalender, um dort eine Aufgabe anzulegen.

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

@@ -261,6 +261,7 @@
   "dayHeadingPattern": "EEEE, d. MMM",
   "overdueHide": "Überfälliges ausblenden",
   "overdueShow": "Überfälliges einblenden",
+  "paneResize": "Größe ändern",
   "planButton": "Plan: {count}",
   "planTitle": "Plan",
   "planShow": "Plan einblenden",