Dry Stone Wall page: `stone-wall/index.html` on the `stone-wall/wall.js` rules, listed in the catalogue and the town #268

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

Done looks like:

• [ ] stone-wall/index.html draws the wall rising across a hillside field from the fixed camera, the pile of stones beside it and the next free position, and drives it only through stone-wall/wall.js; it adds no game rule of its own. Tap a stone in the pile to lay it, tap the wall to undo. Ambient motion only in a sheep grazing beyond the wall. The HUD shows course, stones left and score as the rules state reports them.
• [ ] Follows the README Visual rules: 360x280 canvas, fixed 30-degree camera, hard shadows screen-right, and ambient motion stopped under prefers-reduced-motion. Joints that a placement would stack are marked with a line, not only a colour, and a refused stone is marked with a cross, not a shake. 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: 'stone-wall', title: 'Dry Stone Wall', blurb: 'Lay the stones course by course so no joint sits over another', kind: 'Strategy', input: 'Tap', accent: '#9a8f7a', music: false, forged: true }. It has the matching <li> in the root index.html, a building in the town from town.js like every other game, 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 stone-wall that reaches the end line. serve.test.mjs asserts that /stone-wall/ and /stone-wall/wall.js answer 200. playtest.test.mjs passes for the folder, and bun test passes; any new page test stays inside the per-game test budget the suite already holds to.

Files: stone-wall/index.html, shell.js, index.html, town.js if buildings are listed there, 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.

Waits for #240 (the stone-wall/wall.js rules) to land on main. Replaces #205 and #265, parked only because an issue they once waited on was split.