feat(web): add browser build for TDK Pinball

Expose the existing Macroquad game as a static WASM website while preserving
native desktop behavior. Native-only simulation/file-export code and the
per-user filesystem save path are now separated from the browser build.

The browser version uses a small WASM-only storage support crate and a
Macroquad-compatible JavaScript plugin to persist the same JSON settings and
high scores in localStorage. Browser audio decoding starts in an owned
background coroutine so the game can render its original loading/attract
screens while the embedded sounds finish loading. The checked-in web bundle
contains the optimized WASM, centered black HTML shell, and build/serve
instructions.

Test Plan:
- `just test` -- passed, 135 tests
- `just clippy` -- passed
- `cargo clippy --target wasm32-unknown-unknown -- -D warnings` -- passed
- `cargo +nightly fmt --check` and web-storage format check -- passed
- `just web-build` -- passed; packaged WASM matches the production artifact
- Browser smoke test at `http://127.0.0.1:8000/` -- rendered the centered
  game, started gameplay, opened settings, and restored a changed language
  from browser storage in a fresh page with no runtime errors

tdkpin-rs/web/README.md

@@ -0,0 +1,15 @@
+# TDK Pinball Machine web build
+
+Build and serve the browser version from this directory with:
+
+```sh
+just web-serve
+```
+
+The game is compiled for `wasm32-unknown-unknown` and loaded into the centered
+black canvas by `index.html`. Browser settings and high scores are saved in
+`localStorage`; native builds continue to use their normal per-user save file.
+
+The page uses Macroquad's official browser loader from the miniquad samples
+site. The web page must be served over HTTP rather than opened directly from a
+`file:` URL.