Add dockerized test coverage and CI workflow

[merval]

Motivation

• Provide broad automated unit test coverage for client, config, routes, and service logic to catch regressions early.
• Enable running the same test suite inside a Docker container so CI can validate behavior in a hermetic image.

Description

• Added many new and expanded unit tests under tests/ covering client helpers (tests/test_client.py), config loading (tests/test_config.py), routes (tests/test_routes.py), and services (tests/test_services.py).
• Updated Dockerfile to introduce a test build stage that copies the test suite and runs python -m unittest discover -s tests -v, and kept a separate runtime stage for the app server.
• Added a GitHub Actions workflow .github/workflows/tests.yml that builds the Docker test target and runs the test container on pushes to main, pull requests, and manual dispatch.
• Documented test commands in README.md and added .dockerignore to keep Docker contexts small.

Testing

• Ran python -m unittest discover -s tests -v locally which executed 49 tests and all passed (OK).
• Ran python -m unittest discover -v locally which also executed 49 tests and all passed (OK).
• Verified the CI flow by adding a workflow that builds and runs the Docker test image, and attempted a local Docker build/run but it could not be executed here because Docker is not available in this environment (docker: command not found).

---

Codex Task