ROADMAP.md and STATE.md predate the issue tracker. They were how planning
worked before issues and milestones existed, and keeping them means
maintaining a second copy of that information by hand — which is why
STATE.md still described release/v2.8.0 as the next release, eight minors
ago.
Issues and milestones say the same thing and can't drift: a milestone maps
to its release/vX.Y.Z branch, which is now also how a contributor learns
where to target a PR. Both files stay in git history if a past decision
needs looking up.
Repointed the six references at the tracker: the README's docs list, two
rows in the docs map, PROJECT.md's Current Milestone, and REQUIREMENTS.md's
idea-backlog pointer. ARCHITECTURE.md's "see the roadmap's idea backlog"
now cites the crash reporter's web-issue path instead — a worked example of
the no-network rule beats a pointer to a deleted backlog.