fix(env): stop or kill docker containers on cleanup

[dannyward630]

Summary

Fixes #797.

DockerEnvironment.cleanup() currently falls back from docker stop to docker rm -f. That makes cleanup force removal when stop fails, even though removal is already controlled by the configured run_args (--rm by default) and users may intentionally omit --rm to keep stopped containers for debugging.

This changes the fallback to docker kill, so cleanup attempts to terminate the container while leaving removal policy to Docker's --rm behavior or the user's run_args override.

Validation

• .venv/bin/python -m pytest tests/environments/test_docker.py -k 'config_defaults or cleanup_stops_or_kills'
  • 1 passed, 2 skipped, 20 deselected on this machine because Docker/Podman are not available
• .venv/bin/ruff check src/minisweagent/environments/docker.py tests/environments/test_docker.py
• git diff --check

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