feat: mesh graph tab, routing trace, QR invite, remove all fakes, specialized-node tests

fix: node identity, Gradio 6 chatbot format, peer discovery; add routing+special-node docs; screenshots

feat: impl_ref gaps closed — Nemotron/OpenBMB backends, spec refs, extended UI, HOWTO, multi-node E2E

feat: Phase 2 (M14-M25, X05-X07) + Phase 3 experimental (M26-M31) + E2E tests + docs