Ports n3xd's four: pre-commit, backend tests, sharded Playwright and a
compose smoke test. Everything comes from the committed .env.example, so
no repository secrets are needed; Actions still has to be enabled per
repository and a runner registered with the ubuntu-latest label.
container_name, published ports and image tags are all daemon-global, so
two shards on one runner would fight over them. compose.ci.yml resets
them and tags per project. test-backend keeps the fixed names because it
reaches Postgres from the runner host.
Melvin Strobl
78b9f94cab