Positions had list/create/edit already stubbed as list-only; give it real
forms, with a check mirroring the management_position_implies_staff_position
constraint so a bad combination reads as a form error, not a 500. Roles now
groups by role (excluding the MEMBER everyone holds automatically, which was
just noise), grants via a modal instead of a separate page, and its member
picker is a small typeahead combobox instead of a long native <select>.
Gives clubs a self-service /manage/ area for members, families, teams,
roles, and season memberships, alongside real fee-payment tracking
(FeePayment, record_payment/mark_as_paid/remaining_balance) so a
membership's paid status reflects actual money received instead of a
single manually-set flag.
