ci: tie latest image tag to main

Drop the deployment-specific rollout notes from the README.

.github/workflows/docker-publish.yml

@@ -40,7 +40,10 @@ jobs:
             org.opencontainers.image.title=beacon-server
             org.opencontainers.image.description=Beacon — MeshCore LoRa mesh observation server
             org.opencontainers.image.licenses=AGPL-3.0-or-later
+          flavor: |
+            latest=false
           tags: |
+            type=raw,value=latest,enable=${{ github.ref == 'refs/heads/main' }}
             type=raw,value=dev,enable=${{ github.ref == 'refs/heads/dev' }}
             type=semver,pattern={{version}}
             type=semver,pattern={{major}}.{{minor}}