chore: add release workflow - #13

Adds a manual Release workflow mirroring orpc's, so publishing a new version is a single workflow dispatch instead of a local ritual. It validates the version input, bumps every workspace package, drafts a GitHub release, and publishes both packages to npm with provenance.

Workflow

• Triggered by workflow_dispatch with a required version input plus optional dist-tag, skip-bump, skip-changelog, and skip-git-check flags.
• Rejects malformed versions and the latest preid before touching the repo.
• Prerelease versions like 0.2.0-alpha.1 publish under their preid tag by default; stable versions publish under latest.
• Publishes packages/* only, so the root workspace package is never pushed to npm.

Dependencies

• bumpp and changelogithub added as root dev dependencies, since the workflow runs them through pnpm exec.

Testing

• pnpm run lint passes with the new YAML file.
• A local bumpp -r dry run updated the root and both package manifests, then versions were reverted to 0.0.0.

Before the first run

• Publishing uses --provenance without an npm token, so @openapi-spec/types and @openapi-spec/downgrader need npm trusted publishing configured for this repo and workflow.