feat: add release workflow

[Eomm]

What

Adds a release workflow that publishes fastify-cli to npm from the Actions tab: pick the bump type (patch / minor / major) and the reusable workflow does the rest.

It delegates to the new reusable workflow proposed in fastify/workflows#237, which bumps the version, commits it as Bumped vX.Y.Z, publishes to npm with provenance and creates the GitHub release with generated notes.

Blocked on

• feat: add reusable release workflow workflows#237 must be merged and released first. The uses: reference is currently pinned to that PR's commit SHA and must be repinned to the resulting release tag before this PR is merged (marked with a TODO in the file).
• fastify-cli must be configured as an npm trusted publisher, since the publish authenticates via OIDC rather than an NPM_TOKEN secret.

Notes

The release workflow does not run the test suite; CI already validates every commit on main. There is no release:build script in this package, so that step is a no-op here.

[Eomm]

The release job now runs inside a release deployment environment, so only the approved maintainers can actually release.

Before this is merged, the release environment has to be created in Settings -> Environments with:

• fastify/release as a required reviewer
• Prevent self-review enabled
• deployment branches limited to main

Note that an environment that is referenced but never configured is created automatically with no protection rule at all, so this step is not optional.