Clarify benchmark production limits

[Jason-Doyle]

Summary

• state explicitly that current cold reads and large indexed writes miss normal interactive latency targets
• position warm browser cache hits as a production requirement rather than an optional optimisation
• normalise published JSON and CSV line endings before site deployment
• verify deployed evidence content against the documented SHA-256 hashes in Chromium and mobile tests

Validation

• npm run check
• npm run verify:docs
• npm run site:check
• npx playwright test --config site/playwright.config.ts -g "benchmark page publishes"