Add reusable release-notes preview workflow

[cachafla]

What and why?

Adds a documentation-owned release-notes preview workflow that can be invoked with an immutable validmind/release-notes commit. It validates the source PR, performs the targeted Quarto render, and deploys to a stable per-PR preview URL.

This replaces the temporary ref: edit and paired documentation preview PR lifecycle. A follow-up release-notes PR will dispatch this workflow and surface its result on the release-notes PR.

How to test

• YAML parses locally.
• The follow-up caller PR will be enabled after this workflow lands on documentation:main, then tested against an open release-notes PR.

What needs special review?

• Cross-repository dispatch validation and approved branch prefixes.
• Documentation-owned AWS and read-only source credentials remain in this repository.
• Preview deployments are isolated under pr_previews/release-notes/pr-{number}.

Dependencies, breaking changes, and deployment notes

Merge this PR before enabling the caller workflow in validmind/release-notes. No production deployment behavior changes.

Release notes

N/A — internal CI workflow change.

Checklist

• What and why
• Screenshots or videos (Frontend)
• How to test
• What needs special review
• Dependencies, breaking changes, and deployment notes
• Labels applied
• PR linked to Shortcut
• Unit tests added (Backend)
• Tested locally
• Documentation updated (if required)

[github-actions]

PR Summary

This PR introduces a new GitHub Actions workflow designed for previewing release notes. The workflow is triggered via both workflow_call and repository_dispatch events and accepts inputs such as a commit SHA, branch reference, PR number, and correlation ID. It performs several validations by comparing the provided inputs against the actual release-notes PR details retrieved via the GitHub API. For example, it checks that the commit SHA is valid, that the branch reference uses an approved prefix (either automated/* or codex/*), and that the PR number corresponds to an open PR from the expected repository.

After successful validation, the workflow proceeds to:

• Check out the main repository and the release-notes repository (using sparse checkout to optimize performance).
• Identify changed release directories by computing diffs between commits, which determines the target directories for the preview.
• Verify copyright headers to ensure compliance.
• Set up Quarto (using a pre-release version) and run a test merge for Quarto indexes.
• Seed content from the staging environment through AWS S3 before rendering the target previews with Quarto.
• Deploy the rendered preview to a dedicated S3 bucket path, invalidate the CloudFront cache to ensure updated content, and publish a summary that includes the preview URL.

Additionally, the PR removes a hardcoded branch reference from another workflow file, improving maintainability and ensuring that the docs site is validated against the current main branch of release notes.

Test Suggestions

• Run the workflow with valid inputs and confirm that the preview URL is correctly generated and published.
• Test the workflow with an invalid commit SHA or branch ref to ensure it fails early with appropriate error messages.
• Simulate a PR that is either closed or not from the validmind/release-notes repository to verify that the validations prevent preview deployment.
• Induce errors during the Quarto render step (such as forced warnings or errors) to check that the workflow correctly exits on render failures.
• Verify that the AWS S3 synchronization and CloudFront invalidation steps work as expected by monitoring the deployed preview.

[github-actions]

Validate docs site

✓ INFO: A live preview of the docs site is available — Open the preview

[github-actions]

Lighthouse check results

✓ INFO: No site pages to audit in this PR.

Commit SHA: 1e4ef61