Stage PR #648 release-body remediation

[kerberizer]

Purpose

Stage the production-intended remediation for
archzfs/archzfs#648 after updating
it to current production master.

The candidate merge commit has current production commit 926efc8 as its first
parent and the existing production PR head 7ceed71 as its second parent. The
conflict resolution preserves the current package/test architecture,
package-evidence guidance, corrected release description, current roadmap
review state, and staging procedure while integrating the release-body workflow
and keyring readiness gates.

Validation

• actionlint 1.7.12 with ShellCheck 0.11.0
• git diff --check origin/master...HEAD
• Verified the release-body workflow contains no signing secret, environment,
  asset, tag, title, release-state, or non-note release mutation.
• Verified GitHub Markdown rendering contains no forced <br> elements.
• Verified the net diff is limited to the six intended files.

The package-builder inputs and outputs are unchanged. The ordinary Test
workflow is expected to run because workflow files changed; once it reaches the
builder step it can remain non-blocking under the repository's documented
long-check policy.

Staging result

The separately authorized default-branch metadata test completed successfully:

• Push-path release-body run
• No-op staging Release completion probe
• Completion-triggered reconciliation

The push path changed notes to exactly match the body from current staging
master. After the body was replaced with a temporary sentinel, the no-op
Release completion caused workflow_run reconciliation to restore the body
from current staging master.

Across both paths, all assets and digests, annotated tags, title, release state,
release identity, failover state, and displayed published_at remained
unchanged. No _experimental release or tag was created. The real package
Release workflow remained manually disabled and no package publication ran.

Cleanup restored the original staging body exactly, disabled the test-only
workflows, and returned staging master to production commit 926efc8.
The production-intended candidate remains on this branch; the staging-only
overlay is preserved separately at
experiment/pr-648-release-body-2026-09-18 (267b753).

GitHub records this PR as merged because staging master was temporarily
fast-forwarded through the candidate for the authorized default-branch test.
The ordinary package Test remains non-blocking under the documented long-check
policy because this change does not affect its workflow, inputs, or outputs.