ci: Add v1 release candidate validation

[marandaneto]

💡 Motivation and Context

Issue #207 needs a repeatable release-candidate gate that proves the selected commit passed the full client matrix, SDK compliance, public API checks, and locked package dry runs. It also needs a clear separation between automated readiness and the production soak that must happen over time.

This adds a manual validation workflow. It resolves the requested ref once to an immutable SHA, reruns the local release preflight, verifies all required CI checks plus the eight async/blocking compression compliance jobs on that SHA, and stores a candidate record as an artifact.

The package check uses cargo publish --workspace --dry-run --locked, so it covers the current crate and automatically covers both publishable crates after #183 lands. The release guide now records the prerelease and soak process. This PR does not publish a candidate or claim that production validation elapsed.

Part of #207.

💚 How did you test it?

• scripts/validate-release-candidate.sh
• bash -n scripts/validate-release-candidate.sh scripts/verify-release-candidate-checks.sh
• Parsed and linted .github/workflows/v1-release-candidate.yml
• Confirmed verify-release-candidate-checks.sh 96a3816 rejects the existing commit because it predates the eight-job compliance matrix
• Autoreview passed on b8b58af

📝 Checklist

• I reviewed the submitted code.
• I added validation for the release process.
• I updated the release documentation.
• No breaking change or entry added to the changelog.

If releasing new changes

• Ran sampo add to generate a changeset file