Introduce a new Guess The Rank feature: add guess.html and associated styles and logic. app.js gains video modal utilities (extractYouTubeID, openVideoModal, renderApprovedRunsForLevel) and the full guessing-game flow (modes, round lifecycle, input handling). Refactor existing video-open usage to the new modal and enable showing approved runs in the modal. Update multiple navs and index highlights to link to the new Guess Game. Add CSS for guess UI and responsive tweaks, and adjust some UI copy (e.g. "View Video").
miles