Add CI test workflow and README badge

[Copilot]

No automated test execution existed on commits to main. Adds a GitHub Actions workflow to run the test suite on every push and PR targeting main, and surfaces the result via a README badge.

Changes

• .github/workflows/test.yaml — new workflow triggered on push and pull_request to main; installs SWI-Prolog, then runs make test
• README.md — adds a test-status badge linking to the workflow run history

Original prompt

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This section details on the original issue you should resolve

<issue_title>Run tests on commit to main</issue_title>
<issue_description>Please add a GitHub Action workflow to run the test suite automatically on commit to main and report failures.

The tests are run via the command:

swipl -g "load_files([tests/test_pa]), run_tests" -t halt

which will require SWI-Prolog to be installed in the test environment. There is also a Make target available for convenience:

make test

Please also add a badge to the README displaying the test status.
</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Run tests on commit to main #47

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[simonharris]

Thank you.