Add JSONB attribute member_field_required, migration, Change and Membership code interface for atomic per-field required flag.
- Migrations: vereinfacht_contact_id on members, vereinfacht_* on settings - Mv.Config: Vereinfacht ENV/Settings helpers, vereinfacht_configured?, contact_view_url - Setting: vereinfacht_api_url, api_key, club_id
- Add CycleGenerator module with advisory lock mechanism - Add SetMembershipFeeStartDate change for auto-calculation - Extend Settings with include_joining_cycle and default_membership_fee_type_id - Add scheduled job skeleton for future Oban integration