site: the version, patch notes and every figure come from website/release.jsonThe site's pages are templates, rendered from website/release.json at deploytime by tools/site_release.py (stdlib Python, plain HTML out, no new script onthe pages). Each figure carries its value, unit, conditions, the release it wasmeasured at and the docs page and heading it comes from. Each source line onthe benchmarks page now says which release its figures were measured at;nothing else on the pages changes.The site check now fails if release.json's version is not CHANGELOG.md'snewest, or if a figure's heading is missing from the built docs or its value isnot in that section. A release updates release.json in the same commit asCHANGELOG.md and docs/performance.md.