Add Maypole: the playable page and its place in the catalogue, on the rules in `maypole/pole.js` #369

Make the Maypole rules playable and listed, in the same shape as beach-huts/ and tide-crossing/. Starts once #363 has landed maypole/pole.js.

Done looks like:

• [ ] maypole/index.html draws the maypole with its dancers in a ring and the ribbons braiding down the pole, beside the target pattern. Tap two neighbouring dancers, or pick with the arrow keys and Enter, to swap them; U undoes where the rules allow and R restarts. It drives the game only through the export of pole.js and adds no game rule of its own. The HUD shows level, swaps and par from the rules state, and every swap, 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 (ribbons stirring) held still under prefers-reduced-motion. Ribbon colours are distinguishable by pattern as well as colour; the chosen dancer differs by shape. 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 maypole, title Maypole, kind Puzzle, 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 maypole that reaches the win line, serve.test.mjs asserts /maypole/ and /maypole/pole.js answer 200, a maypole/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: maypole/index.html, maypole/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.