[wiperpaul]

Summary

• Add a Docker build and HTTP smoke test to pull-request CI.
• Verify that the container starts and serves the spanselector application.
• Configure the image for headless startup and add a container health check.
• Exclude local environments, caches, and test artifacts from the Docker build context.
• Keep pre-commit fast by running linting, formatting, type checking, and unit tests locally while leaving package, Docker, and browser checks to CI.
• Add a basic pull request template.

Testing

• uv run pre-commit run --all-files
• uv run pre-commit validate-config
• uv run python scripts/docker_smoke.py
• GitHub Actions runs the package build, Docker smoke test, and Playwright tests in Chromium and Firefox.

Screenshots

Not applicable — these changes affect development and CI infrastructure only.