[P1] GitHub Actions CI (install + lint + test matrix)

[pro-utkarshM]

Tasks

• Workflow: fresh install pip install -e ".[dev]" on Python 3.12 + 3.13.
• Run code2test --help smoke step (guards Feat/the mvp #1 regressions).
• Run pytest (feat: Implement Continuous Learning Engine #5) with mocked LLM.
• Lint (ruff/flake8) + format check.

Acceptance

CI green on PRs; install/import breakage fails the build.