Go envelope v1.155 — access and service-secret UX

Access and service-secret UX refinement.\n\n- Align Access hierarchy, full-width posture strip, responsive layouts, contrast, and truthful role/route state with the target design.\n- Use the canonical open Janus mark and contained, circumference-faded artwork.\n- Add the supplied hero artwork to logged-out landing and protected deep-link login flows.\n- Simplify service-on-machine secret setup, add plain-language glossaries, and harden generated plans, validation, authorization, and preflight behavior.\n\nVerification:\n- go build ./...\n- go vet ./...\n- go test ./...\n- go test -race ./...\n- git diff --check