set_user_role (demote) and admin_delete_user counted ALL admins incl. suspended
ones, so with e.g. 1 active + 1 suspended admin you could demote/delete the only
ACTIVE admin — leaving a single suspended admin who can never sign in → permanent
admin lockout needing DB surgery. Now both guards mirror the (already-correct)
suspend guard: block only when the target is an active admin AND it's the last one
(`not target.is_suspended and count_admins(active_only=True) <= 1`) — which also
correctly still allows removing a SUSPENDED admin while one active admin remains.
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