WASM / Web

[ErikSom]

I took a shot at getting the testbed running in the browser. It's a straightforward Emscripten port. The existing renderer runs unchanged on WebGPU (including the GTAO compute shaders), and the solver runs multithreaded on web workers.

Live demo (needs a WebGPU browser):
https://box3d-7rh.pages.dev/

Diff against current main: ErikSom#1

It's a small change, around 260 lines, all fenced behind if(EMSCRIPTEN) / #ifdef EMSCRIPTEN, so native builds are untouched. The WGSL shaders are generated at build time rather than committed, and I added a CI job that builds the web target alongside the existing ones.

I guess the big question is: what would a wasm version be for? A few directions this could go:

Just a showcase: the testbed as an easily accessible demo of the engine's state, updated with each release.
Dev tooling: e.g., sharing replays/repros as links instead of attachments in bug reports.
An embeddable engine for web games: that's separate from this port, but the testbed proves the core runs well in wasm.
This PR only aims at the first one. Curious what you think.