release: v1.31.1 — docs restructure, SECURITY.md, corrected benchmark figures
No server code change. README rewritten as a landing page, SECURITY.md added
(the README linked a policy that did not exist), and the benchmark docs
corrected: a 100.0% reduction that is actually 99.996%, a grand total that
silently assumed the file is re-read per task, and a stale tokenizer-agreement
claim. The harness is fixed alongside the artifact so regeneration cannot
reintroduce the rounding.
Published to PyPI separately (manual step). If this release is newer than the latest version on PyPI, the PyPI upload has not happened yet.