Rework balances around per-parent days left and deduce the partner from FK

Manual entry now takes one parent's sjukpenningnivå, lägstanivå and
dubbeldagar left (plus optional reserved days) and derives the rest in
build_snapshot, shared with the scraper. The scraper also reads the
family panel and exposes a partner deduction; with two parents it is
saved as a 'deduced' snapshot (migration 002). Parent count is the single
source of entitlement: one member gets 480 days and 96 savable at age 4,
two get 240 and 48 each. Workspaces are capped at two parents.

Also lands the in-flight squash of migrations 002–011 into the initial
schema and the removal of planning_mode.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

backend/app/routers/leave_wishes.py

@@ -48,6 +48,7 @@ async def create_leave_wish(
             parent_mode=payload.parent_mode,
             parent_personal_data_uuid=payload.parent_personal_data_uuid,
             window_mode=payload.window_mode,
+            wants_dubbeldag=payload.wants_dubbeldag,
         )
     except ValidationError as exc:
         raise HTTPException(status.HTTP_422_UNPROCESSABLE_ENTITY, str(exc)) from exc
@@ -96,6 +97,7 @@ async def update_leave_wish(
             parent_mode=payload.parent_mode,
             parent_personal_data_uuid=payload.parent_personal_data_uuid,
             window_mode=payload.window_mode,
+            wants_dubbeldag=payload.wants_dubbeldag,
             _clear_child_id="child_id" in fields_set and payload.child_id is None,
             _clear_last_year="last_year" in fields_set and payload.last_year is None,
             _clear_parent_personal_data_uuid=(