docs: align public evidence with context-boundary research

[tcconnally]

Summary

• align the public claim registry and proof surfaces with the validated 1.0.26 / Vault 2.22.0 evidence posture;
• update the government capability statement to separate QA, retrieval, temporal correctness, scale, and render measurements;
• add context-boundary positioning: attention processes supplied tokens but does not certify provenance, authority, temporal truth, or explanation;
• add the Transformer / long-context / attention-explanation research references to the public benchmark methods page;
• extend claims-sync tests to cover the capability statement, benchmark page, and Vault page.

Verification

• python scripts/render_claims.py --check
• uv run --with pytest python -m pytest -q tests/test_claims_sync.py (3 passed)
• static HTML tag/reference/stale-metric checks passed

The public capability statement route is included in this change. No deployment or merge is performed by this PR.