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/tests/unit/test_leave_wish_repository.py

@@ -275,6 +275,42 @@ class TestSQLiteLeaveWishRepository:
         assert fetched is not None
         assert fetched.target_days is None
 
+    async def test_create_defaults_wants_dubbeldag_to_false(
+        self,
+        leave_wish_repo: SQLiteLeaveWishRepository,
+        seeded_ids: SeededIds,
+    ) -> None:
+        entity = _make(workspace_id=seeded_ids.workspace_id)
+        created = await leave_wish_repo.create(entity)
+        assert created.wants_dubbeldag is False
+
+        fetched = await leave_wish_repo.get_by_id(created.id)
+        assert fetched is not None
+        assert fetched.wants_dubbeldag is False
+
+    async def test_create_and_update_round_trip_wants_dubbeldag(
+        self,
+        leave_wish_repo: SQLiteLeaveWishRepository,
+        seeded_ids: SeededIds,
+    ) -> None:
+        entity = _make(
+            workspace_id=seeded_ids.workspace_id, parent_mode="both", wants_dubbeldag=True
+        )
+        created = await leave_wish_repo.create(entity)
+        assert created.wants_dubbeldag is True
+
+        fetched = await leave_wish_repo.get_by_id(created.id)
+        assert fetched is not None
+        assert fetched.wants_dubbeldag is True
+
+        fetched.wants_dubbeldag = False
+        updated = await leave_wish_repo.update(fetched.id, fetched)
+        assert updated.wants_dubbeldag is False
+
+        refetched = await leave_wish_repo.get_by_id(created.id)
+        assert refetched is not None
+        assert refetched.wants_dubbeldag is False
+
     async def test_get_by_workspace(
         self,
         leave_wish_repo: SQLiteLeaveWishRepository,
@@ -446,6 +482,7 @@ class TestLeaveWishService:
         assert result.target_weeks == 6
         assert result.recurrence == "once"  # default
         assert result.parent_mode == "either"  # default
+        assert result.wants_dubbeldag is False  # default
 
     @pytest.mark.parametrize("recurrence", ["once", "yearly"])
     async def test_create_accepts_valid_recurrence(
@@ -522,6 +559,11 @@ class TestLeaveWishService:
             "last_year",
             id="last_year_before_first_year",
         ),
+        pytest.param(
+            {"parent_mode": "either", "wants_dubbeldag": True},
+            "wants_dubbeldag",
+            id="wants_dubbeldag_forbidden_unless_both",
+        ),
     ]
 
     @pytest.mark.parametrize("overrides,match", _REJECTION_CASES)
@@ -578,6 +620,49 @@ class TestLeaveWishService:
         assert result.parent_mode == "specific"
         assert result.parent_personal_data_uuid == seeded_ids.personal_data_uuid
 
+    # -- wants_dubbeldag (§Decision A, opt-in co-leave) ---------------------
+
+    async def test_create_both_parent_mode_can_opt_into_dubbeldagar(
+        self,
+        leave_wish_service: LeaveWishService,
+        seeded_ids: SeededIds,
+    ) -> None:
+        result = await leave_wish_service.create(
+            workspace_id=seeded_ids.workspace_id,
+            name="Wish",
+            window_start_month=1,
+            window_start_day=1,
+            window_end_month=1,
+            window_end_day=10,
+            target_weeks=1,
+            first_year=2027,
+            parent_mode="both",
+            wants_dubbeldag=True,
+        )
+        assert result.parent_mode == "both"
+        assert result.wants_dubbeldag is True
+
+    async def test_update_can_toggle_wants_dubbeldag(
+        self,
+        leave_wish_service: LeaveWishService,
+        seeded_ids: SeededIds,
+    ) -> None:
+        created = await leave_wish_service.create(
+            workspace_id=seeded_ids.workspace_id,
+            name="Wish",
+            window_start_month=1,
+            window_start_day=1,
+            window_end_month=1,
+            window_end_day=10,
+            target_weeks=1,
+            first_year=2027,
+            parent_mode="both",
+        )
+        assert created.wants_dubbeldag is False
+
+        updated = await leave_wish_service.update(leave_wish_id=created.id, wants_dubbeldag=True)
+        assert updated.wants_dubbeldag is True
+
     # -- window_mode (§10.1) ------------------------------------------------
 
     async def test_create_defaults_to_fixed_window_mode(