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/src/types/api.ts

@@ -45,7 +45,6 @@ export interface WorkspaceCreateRequest {
 
 export interface WorkspaceUpdateRequest {
   name?: string
-  planningGoal?: 'max_time' | 'max_money' | 'balanced'
   planningMode?: 'solo' | 'couple'
 }
 
@@ -86,7 +85,6 @@ export interface LeaveWishCreateRequest {
   priority?: number
   parentMode?: 'either' | 'both' | 'specific'
   parentPersonalDataUuid?: string | null
-  goalOverride?: 'max_time' | 'max_money' | 'balanced' | null
 
   // PLANNING_ENGINE_SPEC.md §10.1 — defaults to 'fixed' server-side when omitted.
   windowMode?: 'fixed' | 'flexible'

frontend/src/types/entities.ts

@@ -4,7 +4,6 @@
 export interface Workspace {
   id: string
   name: string
-  planningGoal: 'max_time' | 'max_money' | 'balanced'
   planningMode: 'solo' | 'couple'
   createdAt: string // ISO-8601
 }
@@ -50,7 +49,6 @@ export interface LeaveWish {
   priority: number
   parentMode: 'either' | 'both' | 'specific'
   parentPersonalDataUuid: string | null
-  goalOverride: 'max_time' | 'max_money' | 'balanced' | null
   // PLANNING_ENGINE_SPEC.md §10.1 — 'fixed': window_start_*/window_end_* are the
   // exact placement. 'flexible': the same fields describe the bounding range the
   // allocator searches within for the best-costing placement.