Added mock test user to auth slice initialState to provide familyId
for children fetching in development environment.
Issue: Tracking pages couldn't fetch children because state.auth.user
was null, resulting in no familyId for API calls.
Solution: Mock user with test familyId in development mode only.
TODO: Implement proper authentication flow in production.
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Co-Authored-By: Claude <noreply@anthropic.com>