Docs: public clarity pass (STATUS, evidence cards, relabelled claims, docs check)

[arybach]

Summary

Documentation only. No code, tags, releases or licence-file changes (the only non-prose edit removes one stray closing code fence in SPEC.md).

What changed

• README: first screen (what it does, who it is for, maturity, 3-minute example, evidence, limitations, naming, docs); first line aligned with the GitHub description.
• Tenant reward table relabelled Illustrative/synthetic (seeded simulators).
• Claims corrected: Go-parity wording withdrawn; test count updated; install line includes the dependencies the tests need; reproducibility notes added to benchmark figures.
• New: STATUS.md (including a versions table), CONTRIBUTING.md, SECURITY.md, CHANGELOG.md (pointer), docs/evidence/ cards, scripts/docs_check.py and a docs-check workflow.

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