- Add AgeValidation module for consistent age checks
- Validate admin contacts must be at least 18 years old
- Move age validation logic from Domain to shared module
- Add tests for admin contact age validation
- Fix JSON format for admin_contacts_allowed_ident_type setting
This change ensures that administrative contacts must be adults (18+),
using the same age validation logic as for registrants. The validation
works with both birthday and Estonian ID formats. Settings are now
properly stored as JSON strings for consistent parsing.
