Feature/add testing workflow

[AchiTsa]

Key Changes

• GitHub Actions Workflows:

  • Created .github/workflows/backend-ci.yml to automate Python testing (pytest) and linting (ruff).
  • Created .github/workflows/frontend-ci.yml to automate Next.js linting, unit testing (jest), and production builds.

• Environment Fixes:

  • Resolved ModuleNotFoundError in the backend by correctly configuring PYTHONPATH: ./backend within the CI environment and local scripts.
  • Addressed Node.js 20 deprecation warnings by opting into the Node.js 24 runner environment.

• Developer Tooling:

  • Added scripts/test_all.sh (Bash) and scripts/test_all.ps1 (PowerShell) to allow developers to run the entire test suite locally with a single command.

• Verification Tests:

  • Added "smoke tests" in tests/test_ci_setup.py and frontend/src/tests/ci_setup.test.ts to verify that the testing infrastructure is healthy.

• Documentation:

  • Added docs/AUTOMATED_TESTING.md with clear instructions on how to run, add, and troubleshoot tests.

Closes #77

[AchiTsa]

@luca55466 could you please review before I remove the Draft.
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