Link planned days to their wish, fix the age-4 cap, drop the planning goal

Three changes that together unblock treating a calendar period as one
editable object.

Migration 008 adds `planned_leave_day.wish_id` (nullable, ON DELETE SET NULL)
so a persisted day knows which `leave_wish` produced it, `is_pinned` to mark a
day the user hand-edited, and `leave_wish.target_days` so a period drawn on a
calendar need not be a whole number of weeks. Apply-time identity still keys on
day_type/is_dubbeldag only, so a wish_id-only difference is a metadata update
rather than a collision.

The age-4 savable ceiling was applying the per-child figure of 96 to each
parent's pool, modelling a two-parent family as able to save 192 days past the
child's fourth birthday. `resolve_age4_savable_cap` is now the single place
that decides 48 (couple with two parents) versus 96 (everyone else), and both
AnalyticsService and the allocator read it.

Migration 009 drops `workspace.planning_goal` and `leave_wish.goal_override`.
The allocator's tier-3 policy collapses to one rule; `salary_type` still
branches, since that reflects what a vacation day actually costs a parent
rather than a user preference.

backend/tests/unit/test_services/test_allocation_input_loader.py

@@ -4,8 +4,8 @@ planning engine (see app.services.allocation_service module docstring).
 Uses the same sqlite-backed fixtures as the rest of the service test suite
 (tests/conftest.py) to seed a realistic workspace and verify the loader nets
 out already-committed `planned_leave_day` rows, falls back to default
-entitlement when no FK snapshot exists, and reads `planning_mode` /
-`planning_goal` off the workspace.
+entitlement when no FK snapshot exists, and reads `planning_mode` off the
+workspace.
 """
 
 from datetime import date, datetime
@@ -91,7 +91,6 @@ class TestAllocationInputLoader:
             Workspace(
                 id=uuid4(),
                 name="Familj",
-                planning_goal="max_money",
                 planning_mode="couple",
                 created_at=now,
             )
@@ -202,8 +201,10 @@ class TestAllocationInputLoader:
         alloc_input = await loader.load(ws.id, today=date(2027, 1, 1))
 
         assert alloc_input.planning_mode == "couple"
-        assert alloc_input.planning_goal == "max_money"
         assert alloc_input.today == date(2027, 1, 1)
+        # Two parents in a 'couple' workspace -> per-parent age-4 cap (48),
+        # not the per-child figure (96).
+        assert alloc_input.age4_savable_cap == 48
 
         pool_with_fetch = alloc_input.pools[(parent_with_fetch.uuid, child.id)]
         assert pool_with_fetch.sjukpenning_left == 288  # 290 - 2 committed
@@ -284,9 +285,7 @@ class TestAllocationInputLoader:
         leave_wish_repo: SQLiteLeaveWishRepository,
     ) -> None:
         now = datetime.now()
-        ws = await workspace_repo.create(
-            Workspace(id=uuid4(), name="Solo", planning_goal="balanced", created_at=now)
-        )
+        ws = await workspace_repo.create(Workspace(id=uuid4(), name="Solo", created_at=now))
         await personal_data_repo.create(
             PersonalData(uuid=uuid4(), workspace_id=ws.id, name="Solo Parent", created_at=now)
         )