Add Paper Route: throw newspapers onto porches from a passing bike #6

A new game in the house style: a short isometric street of three or four houses floating on white, a cyclist riding past at a steady pace.

Done looks like:

• [ ] paper-route/index.html mounted through PixelPlays.mount({ id: 'paper-route', rules }) like the existing games.
• [ ] Tap (or space) throws a paper; the moment you tap decides where it lands, as in Tie-Break. Porch = 3 points, lawn = 1, a window = minus 2 with a broken-pane pixel effect. Ten papers per round; score and best on the HUD.
• [ ] Keyboard and touch both work; canvas aria-label says how to play; 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 /paper-route/ answers 200 text/html; bun test passes.
• [ ] Follows the README Visual rules (hedges/trees sway, stops under prefers-reduced-motion).

Files: paper-route/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.