Release check

Maintainer gate script:

make release-check

Runs scripts/release_check.sh: ruff, pytest, Grafana JSON validation, bash -n on scripts, SMOKE_NO_COMPOSE=1 smoke, make version, changelog/release-doc guards, mkdocs build --strict (make docs-check), optional Compose gates when COMPOSE_INTEGRATION=1, optional FULL_RELEASE_TEST=1 for isolated fresh-volume test.

Use COMPOSE_INTEGRATION=1 before tagging when Compose is available locally.