Website: one engine, three answers; bisect timeline and prerequisites card

run.html shows a release timeline when a share code carries a bisect, with the first bad release marked, and a 'What the docs assume' card when it carries a prerequisite proof, with each item's reason, the proof line and a copyable block. The landing page gets a three-card section linking to real replays. Share codes now carry the prerequisite evidence, step counts and markdown. Includes the site favicon.