Retain v0.3.0 post-release receipts

[regenrek]

Summary

• update the Planr hard-cut handoff to the reviewed v0.3.0 release receipt
• add the v0.3.0 publication certification receipt
• retain final-candidate live host JSON evidence under tracked retained-evidence paths

Verification

• git diff --check
• sh scripts/check-migration-manifest.sh
• jq assertions for retained v0.3.0 candidate/native package digest and Codex/Cursor receipt correlation
• protected Planr repo baseline remained unchanged

No tag, release, npm package, Homebrew formula, or website deployment was changed.

[regenrek]

Findings-first review: no blocking findings in the focused post-release receipt diff. Scope is limited to durable receipt docs and retained v0.3.0 candidate evidence; no tag, release, npm, Homebrew, website, or Planr product state is changed. CI is green as of Release Candidate run 29860769223, CI run 29860777436, and Secret Scan run 29860777234.