Add Hopscotch: the playable page and its place in the catalogue, on the rules in `hopscotch/court.js` #376

Make the Hopscotch rules playable and listed, in the same shape as apple-bobbing/. Starts once the Hopscotch rules issue has landed hopscotch/court.js.

Done looks like:

• [ ] hopscotch/index.html draws the chalk court, the stone, the player and the power meter sweeping by meter(state, tick). Space, Enter or a tap tosses; arrow keys or a tap on a square hop; R restarts. It drives the game only through the export of court.js and adds no game rule of its own. The HUD reads from the rules state, and every move, refusal and end line is announced through an aria-live region.
• [ ] Follows the README Visual rules: 360x280 canvas via engine.js, fixed 30-degree camera, hard shadows screen-right, ambient motion (leaves) held still under prefers-reduced-motion; the meter itself keeps sweeping since it is the game, and the page says so. The canvas aria-label says how to play, the rules popup is at most four lines, there is a #mute button and no .mp3 is committed.
• [ ] Listed in GAMES in shell.js with id hopscotch, title Hopscotch, kind Timing, input Tap, music: false and forged: true; the matching <li> in the root index.html; in the README Games table and the list of games without music; bun scripts/og.mjs has been run.
• [ ] rounds.mjs has a scripted round for hopscotch that reaches an end line, serve.test.mjs asserts /hopscotch/ and /hopscotch/court.js answer 200, a hopscotch/page.test.mjs stays inside the per-game test budget, playtest.test.mjs passes for the folder, and bun test passes. bun scripts/design-lint.ts passes.

Files: hopscotch/index.html, hopscotch/page.test.mjs, shell.js, index.html, README.md, rounds.mjs, serve.test.mjs, og/. Risk: shared files with every other page pull; rebase before pushing. Fits: a builder.