Run CI on main and on stacked pull requests

[JedimEmO]

Follow-up to #22/#23, which both merged without a single check run. This closes the two gaps that allowed it.

What went wrong

rust.yml triggered only on pull_request with branches: [main].

1. main is never tested. There is no push trigger, so anything reaching main by another route is unverified. The run history shows Code checking and unit testing firing for modernize-example-app (Rebuild the example site as a bleeding-edge dwind/dominator showcase #21) and then nothing for Let dwind express keyframes, pseudo-elements and arbitrary declarations #22 or Delete the example's stylesheet #23 — the pushes to main only triggered the Pages deploy.
2. Stacked PRs get no checks. A PR based on another feature branch doesn't match branches: [main]. Let dwind express keyframes, pseudo-elements and arbitrary declarations #22 was based on modernize-example-app and Delete the example's stylesheet #23 on dwind-keyframes-and-arbitrary-values, so neither ever qualified. They were retargeted to main shortly before merge, which is too late for checks to run.

The changes that most want verifying are the stacked ones, since they land on top of an unmerged base.

The change

on:
  push:
    branches: [ main ]
  pull_request:
  workflow_dispatch:

push stays pinned to main, so a PR branch in this repo doesn't run twice. workflow_dispatch means main can be re-checked on demand instead of needing a throwaway PR.

Verification

The workflow was run locally against merged main, reproducing all four steps:

step	result
cargo test (host)	pass
cargo clippy	pass
wasm suite, Firefox	pass
wasm suite, Chrome	pass

Two notes from doing that, both worth knowing for anyone reproducing CI locally:

• It needs wasm-bindgen-cli 0.2.105 to match Cargo.lock. A newer global install fails with a bindgen schema mismatch — which is exactly what the existing comment on the wasm-bindgen-action version pin is warning about. wasm-pack test masks this by managing its own matching copy, so the bare cargo test --target wasm32-unknown-unknown that CI runs is the stricter check.
• The Chrome leg needs a ChromeDriver matching the installed Chrome (149 here).

This PR is itself the first test of the new trigger: opening it should produce a check run.

🤖 Generated with Claude Code