docs: refresh pre-visibility evidence

[tensornull]

What changed

• Record the completed dispositions of superseded dependency pull requests.
• Replace initial PR Complete Public Preview pre-visibility validation #9 evidence with final-head, squash-merge, and default-branch CI evidence.
• Record PR docs: define topic branch lifecycle #10, the latest private default-branch CI, fail-closed Release Please behavior, and current remote evidence boundaries.
• Add the final 2026-07-23 local package, self-containment, public-content, secret, and workflow validation record.

Why

The roadmap still described already-completed dependency cleanup as future work and did not capture the final remote evidence now required for a self-contained pre-visibility handoff.

Validation

• Independent milestone-contract review: no findings after revisions
• Independent remote fact audit: no findings after revisions
• Complete local gate from AGENTS.md and RELEASING.md
• 200 offline tests passed; one live test deselected
• Fresh wheel and sdist passed metadata, artifact, and independent clean-install checks
• Copied standalone repository verification passed
• actionlint 1.7.12 passed online-cache and offline modes