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/useBreakPeriods.ts

@@ -41,9 +41,9 @@ export function useBreakPeriods(workspaceId: string | null): UseBreakPeriodsResu
       if (!workspaceId) throw new Error('Workspace not selected')
       const result = await api.createBreakPeriod(workspaceId, {
         name,
-        start_date: startDate,
-        end_date: endDate,
-        target_weeks: targetWeeks,
+        startDate,
+        endDate,
+        targetWeeks,
       })
       await fetch()
       return result