Peering: sync with configured peers via NIP-77 reconciliation and a live feed #935

Part of the relay peering work in #931.

Scope

Wire the transfer of events between configured, authenticated peers using existing primitives — no new wire protocol:

• On establishing a peering relationship, reconcile history with a NIP-77 negentropy session scoped to the agreed feed scope, so a new or restarted peer catches up without a full dump.
• Stay current with a live subscription for the feed scope.
• Build the peer sync path on NIP-77 directly: the StaticMirroringWorker was removed in chore: sunset the StaticMirroringWorker #924, so there is no existing mirroring machinery to reuse. The authenticated peer identity (Peering: authenticate peer relays with NIP-42 using the relay's own keypair #933) and the terms/scope from the advertisement (Peering: advertise peering terms and scopes in the NIP-11 document #932) take the place of static mirroring's config-file peer list — one sync design driven by the peering advertisement, not a second engine.

Acceptance

• A peer that starts empty converges to the source's state within the agreed scope via negentropy.
• Events published to the source after sync arrive at the peer live.
• Sync state per peer (last reconciliation, lag) is recorded for the admin console.