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/models/leave_wish.py

@@ -46,6 +46,10 @@ class LeaveWishCreate(BaseModel):
     # bounding range the allocator searches within for the best-costing window.
     window_mode: str = "fixed"  # 'fixed' | 'flexible'
 
+    # §Decision A (co-leave) — opt-in dubbeldagar; see app/entities/leave_wish.py.
+    # Only meaningful when parent_mode == 'both'.
+    wants_dubbeldag: bool = False
+
 
 class LeaveWishUpdate(BaseModel):
     """Partial update — all fields optional; only provided fields are changed."""
@@ -78,6 +82,11 @@ class LeaveWishUpdate(BaseModel):
 
     window_mode: str | None = None  # 'fixed' | 'flexible'
 
+    # `None` means "leave unchanged" here too, same as every other field on
+    # this partial-update model -- there is no "clear it back to False" need
+    # (False is already the shape-level default), so no `_clear_*` flag.
+    wants_dubbeldag: bool | None = None
+
 
 class LeaveWishResponse(BaseModel):
     id: UUID
@@ -103,6 +112,8 @@ class LeaveWishResponse(BaseModel):
 
     window_mode: str
 
+    wants_dubbeldag: bool
+
     created_at: datetime | None
     updated_at: datetime | None
 
@@ -127,6 +138,7 @@ class LeaveWishResponse(BaseModel):
             parent_mode=entity.parent_mode,
             parent_personal_data_uuid=entity.parent_personal_data_uuid,
             window_mode=entity.window_mode,
+            wants_dubbeldag=entity.wants_dubbeldag,
             created_at=entity.created_at,
             updated_at=entity.updated_at,
         )