Peer-to-peer replication over iroh.
Every yaiba instance is a full replica. Syncing is symmetric — no
peer is authoritative and none has to be reachable at a fixed
address. iroh dials by public key and hole-punches, so peers need
outbound UDP and nothing else: no port forwarding, no inbound rule.
When hole punching fails the connection falls back to a relay, which
only forwards already-encrypted QUIC and cannot read the contents.
Membership is a shared 32-byte room key, handed around inside a ticket. A peer that can't present it is dropped before any data moves.