[Enhancement] Add basic CI pipeline (GitHub Actions) and pytest infrastructure

[pigeio]

Summary

• What changed: Added a foundational CI/CD pipeline using GitHub Actions ([.github/workflows/python-app.yml]). The workflow installs dependencies, runs flake8 for syntax errors, and executes a newly added pytest suite.

• Why: To automatically verify code integrity on all new Pull Requests and pushes to main/mac-port. This prevents regressions, catches syntax errors early, and reduces the manual testing burden on maintainers. Includes [pytest.ini] and a basic API test ([tests/test_api_basics.py] to demonstrate the live testing pipeline.

Related issues

• Issue exists and is linked
• Closes [Task] Add CI/CD Pipeline (GitHub Actions) and Pytest Infrastructure #112
• Related #

Validation

• Tests added/updated (or not applicable)
• Validation steps documented
• Evidence attached (logs/screenshots/output as relevant)

Validation:
When this PR is opened, the GitHub Actions tab will automatically boot an Ubuntu runner, install Python 3.10 and pytest, and execute pytest tests/test_api_basics.py. Evidence is visible directly in the "Checks" section below this PR description.

Documentation

• Docs updated in this PR (or not applicable)
• Any setup/workflow changes reflected in repo docs

Scope check

• No unrelated refactors
• Implemented from a feature branch
• Change is deliverable without upstream OSeMOSYS/MUIO dependency
• Base repo/branch is EAPD-DRB/MUIOGO:main (not upstream)

[SeaCelo]

@pigeio
Closing this in favor of #120 as the single active CI path.

This PR is cleaner and narrower, and the simple Flask request-level smoke test here is useful. But I do not want to keep two overlapping CI PRs active in parallel.

I’m choosing #120 as the surviving CI path because it is the stronger long-term base and already handles the current requirements.txt encoding issue in CI.

That said, the request-level test idea in this PR is still valuable. If #120 lands without an equivalent app-level smoke test, a small follow-up PR that adds that test on top of the merged CI baseline would still be welcome.