Polish repo onboarding and add CI

[IgnazioDS]

What changed

• add a GitHub Actions CI workflow for lint, type-checking, migrations, and pytest
• add README badges, a real request-path architecture diagram, and a clearer 10-minute evaluation path
• add a dedicated docs/build-your-first-agent.md walkthrough from clone to customization to verification
• fix packaging so editable installs work with modern pip/setuptools
• clean up existing Ruff and MyPy issues so the new CI workflow can pass

Why

The repository already had strong technical substance, but it was missing the trust signals and onboarding assets that make a strong starter easier to evaluate quickly.

Validation

• ruff check app/ tests/ scripts/
• mypy app/ --ignore-missing-imports
• pytest -q tests/test_graph/test_nodes.py
• full migration-backed pytest suite could not be run locally because the Docker daemon is not available in this environment

[chatgpt-codex-connector]

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