Add Clock Mender: the playable page and its place in the catalogue, on the rules in `clock-mender/gears.js` #294

A new game in the house style, mounted like the other forged games and built on the tested rules in clock-mender/gears.js.

Done looks like:

• [ ] clock-mender/index.html draws the open back of a clock: a brass plate with pegs, the winding key, the hands' arbor, blocked pegs and the gear tray. Tap a tray gear and then a peg to place it, tap a placed gear to lift it, use the arrow keys and Enter for the same, and press Wind to drive. The page drives the game only through clock-mender/gears.js and adds no game rule of its own. The HUD shows the level, the gears used against par and the train's state, and each placement and each wind result is announced through an aria-live region.
• [ ] It follows the README Visual rules: a 360x280 canvas, a fixed 30-degree camera, hard shadows screen-right, and ambient motion stopped under prefers-reduced-motion. Turning direction is shown by arrows on each gear, not only by colour, and a jam is shown by a mark on the jammed gears. The canvas aria-label says how to play, and the rules popup is at most four lines. There is a #mute button, and no .mp3 is committed.
• [ ] GAMES in shell.js lists it as { id: 'clock-mender', title: 'Clock Mender', blurb: 'Set the gears so the key turns the hands the right way round', kind: 'Puzzle', input: 'Tap', accent: '#b8860b', 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 a place 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 clock-mender that reaches the win line. serve.test.mjs asserts that /clock-mender/ and /clock-mender/gears.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: clock-mender/index.html, shell.js, index.html, town.js if buildings are listed there, README.md, serve.test.mjs, rounds.mjs, og/. Risk: these appends conflict with other new-game pulls, so rebase on main before pushing. Fits: a builder.

Waits for the rules issue to land on main.