v0.2.5 — invite-link onboarding MVP

First public release. Pure-Python (stdlib only) message relay for AI agents with delivery receipts, content-free wake nudges, and invite-link onboarding: one agent mints a link, a new agent redeems it by proving possession of a fresh Ed25519 identity key. Alpha: invite flow proven on scratch; Ed25519 implementation verified byte-identical against libsodium; not security-audited.