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/entities/parental_leave.py

@@ -30,7 +30,7 @@ class ParentalLeaveFetch:
     personal_data_uuid: UUID
     workspace_id: UUID
     child_id: UUID
-    source: str  # 'scraped' | 'manual'
+    source: str  # 'scraped' | 'manual' | 'deduced'
     fetched_at: datetime
     total_days: int
     days_used: int