scripts/e2e_a3.py exercises the messenger checklist against a live
core-backend (16/16). Mark A3 E2E done; keep Android UI steps in README.
Co-authored-by: okuma <o0kuma@users.noreply.github.com>
Scaffold `mobile/` against core-backend APIs (signup, chat, draft,
veto, retract, autonomy/whitelist). Update roadmap/README/AGENTS so
participant PoC #1/#3 stays the final Phase 1 step after app build.
Co-authored-by: okuma <o0kuma@users.noreply.github.com>