Add Kite Hill: keep a kite in the air through 60 seconds of gusts #5

A new game in the house style: a grassy hilltop floating on white, a figure holding a kite line.

Done looks like:

• [ ] kite-hill/index.html mounted through PixelPlays.mount({ id: 'kite-hill', rules }) like the existing games, using engine.js wind and figures.
• [ ] Hold to pull the line (kite climbs, line tension rises), release to let out line; gusts arrive visibly in the grass first. Too much tension snaps the line, too little drops the kite. Score is seconds aloft plus height, over a 60-second round, with a best shown on the HUD.
• [ ] Keyboard (space) and touch both work; the canvas has an aria-label that says how to play; the rules popup is at most four lines.
• [ ] In GAMES in shell.js and the README Games table; has #mute; runs with no .mp3 committed.
• [ ] serve.test.mjs asserts /kite-hill/ answers 200 text/html; bun test passes.
• [ ] Follows the README Visual rules; grass sway stops under prefers-reduced-motion.

Files: kite-hill/index.html, shell.js, README.md, serve.test.mjs. Risk: one-line conflicts with the other new-game issues in shared lists. Fits: a builder.