fix(roadtrip): keep a booked night out of the day list, and off the traveller's stops

Three things the first pass got wrong.

A stop a booking puts on the day is for road trip mode, which needs the
hotel in the driving chain. The day planner already shows that booking as
its own overnight block, so the row there would be the same hotel twice.
It is hidden in Days whatever the service-stop switch says, and the switch
goes back to meaning what it says: the petrol stations the traveller added.

Cancelling a night from the road trip popup took the stop with it. That
control means "this is a pause now, not a night", and the stop sits
mid-drive where re-adding it would land it at the end of the day. The
booking now hands the stop over instead of deleting it.

Moving a booking whose stop belongs to the traveller put a second one on
the new day and left the first behind, which is the duplicate this change
exists to remove. Only a booking's own stop moves now. Stays booked before
this shipped get theirs from the migration, not from the next edit they
happen to receive.

shared/src/assignment/assignment.schema.ts

@@ -48,6 +48,11 @@ export const assignmentSchema = z.object({
   // not a place (booking arrival / morning hotel). null = inherit the day default.
   // Inert when the previous timeline element is a place.
   incoming_leg_transport_mode: z.string().nullable().optional(),
+  // The lodging booking that put this stop on the day, when one did. The day
+  // planner already shows that booking as its own overnight block, so it hides
+  // this row and leaves it to road trip mode, which is the view that needs the
+  // hotel in the driving chain. Null for every stop a traveller placed.
+  accommodation_id: z.number().nullable().optional(),
   participants: z.array(assignmentParticipantSchema).optional(),
   created_at: z.string().optional(),
   place: assignmentPlaceSchema,