chore(release): prepare the v0.9.0 release candidate

[akoita]

Parent: #76

Outcome

Prepare the exact v0.9.0 revision and reproducible release metadata after the workflow-parity rollup is complete.

Scope

• Update version and release metadata for v0.9.0.
• Run pnpm release:preflight from the exact candidate revision before any release action.
• Prepare manifests, checksums, SBOM, package-size evidence, rollback guidance, and known limitations.
• Exercise the supported Linux, macOS, and Windows release acceptance workflow without overstating unavailable platform or representative evidence.

Non-goals

• Merging or dispatching the release workflow without explicit user approval.
• Signing, automatic updates, or unrelated release-infrastructure changes.
• Changing product behavior.

Acceptance criteria

• eval(pilot): demonstrate parity with the proven manual CV workflow #75 is closed with acceptable parity evidence.
• The exact candidate revision passes the mandatory local release preflight.
• Release metadata is internally consistent and deterministic checks pass.
• Required hosted acceptance is ready to run from the candidate revision.
• pnpm validate passes.

Dependencies

• eval(pilot): demonstrate parity with the proven manual CV workflow #75, after eval(pilot): predeclare the v0.9 consented comparison gate #248 and eval(pilot): record one consented v0.9 workflow-parity result #249.