Add Scala.js WebAssembly example to web examples documentation

[yadavshubham01]

This PR adds a new example project demonstrating Scala.js WebAssembly support (introduced in Scala.js v1.17.0). The "Hello World" example shows how to compile Scala.js to WebAssembly using Mill and run it in a browser. It also updates the scalalib/web-examples.adoc with instructions for setting up and running the example.

Key Changes
Added example/scalalib/web/hello-world-wasm with Mill build and Scala.js WebAssembly code.
Updated documentation in scalalib/web-examples.adoc to include steps for building and running the example.

[yadavshubham01]

@lihaoyi please review this PR

[lihaoyi]

@yadavshubham01 This PR does not appear to satisfy the original ticket, there is no webassembly here neither is it integrated into the example docs

[yadavshubham01]

hey @lihaoyi i think we're trying to add a new example to demonstrate how to use Mill with Scala.js to compile to WebAssembly (Wasm) ??

[Quafadas]

@yadavshubham01 I think your interpretation of the goal is correct...

... Unfortunately, this PR does not generate webassembly. It is not (at all) close to doing so. There are a couple of hints in the solution you propose, that make it look as though you are trusting an AI go work through the conceptual challenges on your behalf.

Further, I would advise you that I find tagging a maintainer before the CI has gone green, or unless you are asking for advice poor etiquette. Their time is limited.

I will tell you freely upfront : this approach will not work.

As a courtesy, I'll sketch (my understanding) of the solution below, but you will need to invest your own time in developing a semantic understanding of mill. If your goal it to learn about mill, you'll find people willing to help on the journey. If your goal is to collect 500USD through AI, I would guarantee you'll find this a particularly poor time investment.

Here is the solution sketch;

1. Succeed in generating and running webassembly in a different scala environment. I think right now you'll have to use SBT, although as part of this I would also propose checking if scala-cli can emit WASM yet, and PRing the change to scala-cli. It's arguably outside the scope of this although I suspect you'll find it makes life easier long run.
2. At this point, you'll have enough understanding to differentiate between when you're emitting JS vs WASM. You'll be able to write a failing (integration) test in mills scala-js integration test module
3. Now you'll need to tag a maintainer, to discuss the nomenclature of the public API of the scala JS module and how to configure it to emit webassembly.
4. Now drill the new flag through the scalaJsWorkerAPI, into the scalaJSworker, where you'll configure the linker to emit WASM.
5. Bonus points: throw an exception if the scala JS version is incompatible with WASM
6. Run trivial WASM program to check that it all actually worked and validate that in CI.
7. Write the example into the docs

Step 7 is now trivial.

You'll observe that your current PR misses steps 1-6.