Record 9.3 and 9.4 as merged, and changelog the claim corrections

[404SecNotFound]

Docs only. It closes out Sections 00 to 05 of the current run.

Changes

• docs/ROADMAP.md, Phase 9 status table. I checked each row against main's tree, not the PR badge.
  • 9.4 merged: PR Give each secret buffer one owner that erases it (roadmap 9.4) #227, 2adefa3.
  • 9.3 merged: PR Land roadmap 9.3 on main (PR #228 merged into its stacked base, not main) #229, 6aff83d. PR Write a new backup's ways in with one operation (roadmap 9.3) #228 was merged into its stacked base branch rather than main, so Land roadmap 9.3 on main (PR #228 merged into its stacked base, not main) #229 carried the same commit 487f8be.
• CHANGELOG.md gets the entry for PR Say what the verification, erasure and sealed claims actually establish #225's claim corrections. It was held back from Say what the verification, erasure and sealed claims actually establish #225 to avoid a conflict with Derive every description of a backup's ways in from one access policy #224's entry.

Checks

• test:readme exits 0 (42 scripts documented, audit scope matches).
• test:release-notes exits 0.
• main was merged into this branch, and the diff against main is these two files only.

Next action

The owner merges. Sections 06 onward are outside this run's scope.