Unauthenticated /peer/accept must not overwrite hmac_secret for peers in
needs_attention, same as active. needs_attention means 'auth trust broke
and we don't know why' — letting an unauthenticated request flip it back
would reintroduce a path for silent HMAC rotation via the outbox-401 loop
the rest of #19 closes. Legitimate recovery is the admin 'Reset peering'
action (next task).