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.

frontend/tests/fixtures/mockData.ts

@@ -29,7 +29,6 @@ export function makeWorkspace(overrides: Partial<Workspace> = {}): Workspace {
   return {
     id: 'ws-1',
     name: 'Familjen Testsson',
-    planningGoal: 'balanced',
     planningMode: 'solo',
     createdAt: '2026-01-01T00:00:00',
     ...overrides,
@@ -147,7 +146,6 @@ export function makeLeaveWish(overrides: Partial<LeaveWish> = {}): LeaveWish {
     priority: 1,
     parentMode: 'either',
     parentPersonalDataUuid: null,
-    goalOverride: null,
     windowMode: 'fixed',
     createdAt: '2026-01-01T00:00:00',
     updatedAt: '2026-01-01T00:00:00',