Add Rock Pool: the playable page and its place in the catalogue, on the rules in `rock-pool/pool.js` #199

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

Done looks like:

• [x] rock-pool/index.html draws the tide pool from the fixed camera, its rocks, the crabs as they dash and the bucket, and drives it only through rock-pool/pool.js; it adds no game rule of its own. Tap a crab to scoop it. Ambient motion only in the water shimmering at the edge. The HUD shows tide left, crabs caught and score as the rules state reports them.
• [x] Follows the README Visual rules: 360x280 canvas, fixed 30-degree camera, hard shadows screen-right, and ambient motion stopped under prefers-reduced-motion. A crab in the open is marked by shape (a raised claw outline) as well as colour. 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.
• [x] Listed in GAMES in shell.js as { id: 'rock-pool', title: 'Rock Pool', blurb: 'Scoop the darting crabs into your bucket before the tide comes back', kind: 'Catching', input: 'Tap', accent: '#3a8fa3', 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.
• [x] rounds.mjs has a scripted round for rock-pool that reaches the end line. serve.test.mjs asserts that /rock-pool/ and /rock-pool/pool.js answer 200. playtest.test.mjs passes for the folder, and bun test passes.

Files: rock-pool/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.

Reviewed pull #253 at its head: ticked rock-pool/index.html draws the tide pool from the fixed camera, its rocks, the crabs as they dash and the bucket, and drives it only through rock-pool/pool.js; it adds no game rule of its own. Tap a crab to scoop it. Ambient motion only in the water shimmering at the edge. The HUD shows tide left, crabs caught 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. A crab in the open is marked by shape (a raised claw outline) as well as colour. 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: 'rock-pool', title: 'Rock Pool', blurb: 'Scoop the darting crabs into your bucket before the tide comes back', kind: 'Catching', input: 'Tap', accent: '#3a8fa3', 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 rock-pool that reaches the end line. serve.test.mjs asserts that /rock-pool/ and /rock-pool/pool.js answer 200. playtest.test.mjs passes for the folder, and bun test passes..