Add Hoopla Stall: the playable page and its place in the catalogue, on the rules in `hoopla/hoop.js` #135

A new game in the house style, mounted like the other forged games, built on the tested rules in hoopla/hoop.js.

Done looks like:

• [ ] hoopla/index.html draws the stall and drives it only through hoopla/hoop.js. It adds no game rule of its own. To toss a ring, drag back and release; or use Left and Right to aim, hold Space to build power, and release to toss. Ambient motion only in the stall's bunting. The HUD and end line show what the rules state reports.
• [ ] Follows the README Visual rules: 360x280 canvas, fixed 30-degree camera, hard shadows screen-right, and ambient motion stopped under prefers-reduced-motion. 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 as { id: 'hoopla', title: 'Hoopla Stall', blurb: 'Drag and release to toss rings over the prize blocks, eight rings a round', kind: 'Throwing', input: 'Drag', accent: '#b0533a', music: false, forged: true }. It has the matching <li> in the root index.html, and appears 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 hoopla that reaches the end line. serve.test.mjs asserts that /hoopla/ and /hoopla/hoop.js answer 200. playtest.test.mjs passes for the folder, and bun test passes.

Files: hoopla/index.html, shell.js, index.html, README.md, serve.test.mjs, rounds.mjs, og/. Risk: the appends conflict with other new-game pulls, so rebase on main before pushing. Fits: a builder.