Add release-to-X workflow

[ocque41]

Summary

• Add a GitHub Actions workflow that posts published GitHub Releases to X.
• Add the Node script used by the workflow, including manual dry-run support.

Validation

• Ran node --check scripts/post-github-release-to-x.mjs in this repo.
• Verified the copied script with a local dry run in the rollout batch.

Notes

• Requires the X Actions secrets to be available to this repo: X_API_KEY, X_API_KEY_SECRET, X_ACCESS_TOKEN, and X_ACCESS_TOKEN_SECRET.
• First validation after merge should be a manual Post release to X run with dry_run=true.