[Task]: Add CI workflow for lint + tests

[DYAI2025]

Task Description

Add a GitHub Actions workflow that runs Black (check), flake8, and pytest on pull requests and pushes to main.

Detailed Steps

• Create .github/workflows/ci.yml with jobs for Python 3.12
• Install deps: pip install -r dashboard/requirements.txt if file exists; otherwise install pytest flake8 black
• Run black --check .
• Run flake8 .
• Run pytest -q becoin_economy
• Cache pip between runs
• Trigger on pull_request and push to main

Acceptance Criteria

• CI runs on new PRs and main pushes
• Lint and test steps execute successfully
• Workflow file is documented in README (badges optional)

Complexity

simple