Polish optional FastAPI addon docs and packaging

[nova-rey]

Summary

• include pydantic in the optional api extra while keeping the FastAPI layer opt-in
• refresh API overview, roadmap, and design intent docs with [api] install, run, and curl guidance
• add README cross-links and a Phase 8 report capturing validation notes and follow-ups

Testing

• PYTHONPATH=. pytest -q

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Codex Task

[chatgpt-codex-connector]

💡 Codex Review

crapssim/README.md

Lines 77 to 85 in 34ddfe1

	## Optional Local API
	The project ships with an opt-in HTTP API that simply wraps the existing
	simulator objects for external tooling. It adds a thin control-and-state surface
	that plays nicely with CSC workflows, dashboards, or automation scripts without
	changing how the core engine behaves. No additional runtime dependencies are
	introduced unless you install the optional extras (for example via
	`pip install "crapssim[api]"`).

Document install command for non-existent api extra

The updated docs instruct users to install the API layer via pip install "crapssim[api]", but the packaged project does not expose an api extra—setup.cfg only defines a testing extra and the repository has no build configuration that consumes pyproject.toml’s project.optional-dependencies. Running the advertised command against the released wheel or a local checkout therefore raises ExtrasRequirementError: crapssim 0.x has no such extra 'api', leaving the API addon impossible to install as described. Either add an api extra to the packaging metadata or revert the documentation to a working install path.

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