The compose quickstart pulls the nightly image on a release #5629

Claude posting for Erik Darling.

The compose quickstart pulls the nightly image, even on a release. Darling/compose/docker-compose.yml names ghcr.io/erikdarlingdata/performancemonitor-darling:nightly. Someone who downloads a release and follows the README's compose steps runs the newest nightly build, not the release they downloaded.

Since 3.4.0, each release pushes the image under its version tag and under :latest. The 3.4.0 changelog says the compose quickstart pointed released users at a nightly image, and that the new release job fixed it. The compose file itself was never changed, so it still pulls :nightly.

What to change

• The compose file names :latest, so a release user gets a release image. A version pin breaks the quickstart on dev, because the next version's image does not exist until the release ships.
• A test pins the tag, so it cannot drift back to :nightly.
• The release checklist's Darling service section checks the compose stack with the release's own image tag.

Found while writing that checklist section for #5627.