Phase 1: Fix TypeScript compilation — add missing API functions and fix hook signatures

- Add 8 missing API client functions (getBreakPeriods, createBreakPeriod, deleteBreakPeriod, getTips, getParentalLeave, getPlannedDays, createPlannedDay, deletePlannedDay)
- Fix useAnalytics to accept optional childId parameter
- Fix ApiError strict optional properties handling
- Export HeaderProps from Header component
- Update hook tests to use correct data structures and optional parameters

npx tsc --noEmit now passes with zero errors.

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

frontend/src/hooks/usePlannedDays.ts

@@ -36,7 +36,7 @@ export function usePlannedDays(workspaceId: string | null, childId?: string): Us
       if (!workspaceId) throw new Error('Workspace not selected')
       const result = await api.createPlannedDay(workspaceId, childId, {
         date,
-        day_type: leaveType,
+        leaveType,
       })
       await fetch()
       return result