feat(todo): Upcoming's tasks dragged onto another day (ADR 0033, D16)

A row of Upcoming, overdue ones too, held and dropped on another day
moves there, its time, duration and recurrence kept; Moved to … offers
Undo. The tint over a day a drag hovers is laid beside the rows, not
around them, which paint on the Material beneath.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Tizian 「ティツィアーン」 <raisondetredev@pm.me>

docs/adr/0033-halkyon-todo.md

@@ -235,9 +235,10 @@ alternative was put to them, the choice is theirs.
   is dragged straight away, without a hold, its place meanwhile a larger × where
   dropping it gives up: dropped between a project's rows, quick add adds there (each
   next task below the one before); on a day in Upcoming, for that day; on Today, for
-  today. Today's and Upcoming's rows aren't dragged, their order being their dates',
-  times' and priorities'.
-- **To come**: dragging a task onto another day in Upcoming.
+  today. Upcoming's rows, overdue ones too, held and dropped on another day move there,
+  their time, duration and recurrence kept, *Moved to …* offering to undo it; their
+  order within a day stays their times' and priorities', and Today's rows aren't
+  dragged.
 
 ## Steps