feat(chip-viewer): add a browser target

[Lfan-ke]

chip-viewer-native cannot be built for wasm32: main.rs parses CLI arguments and chip-view-db memory-maps its input. This adds chip-viewer-wasm, which keeps the portable half — the layer styling in chip-display, whose only dependency is chipgeom-format — behind an eframe app the host page mounts on a canvas.

chip-viewer-native is untouched.

Verification

cargo check -p chip-viewer-wasm --target wasm32-unknown-unknown   Finished
cargo check --workspace                                           Finished
cargo fmt --all -- --check                                        clean

The new CI step runs the first of these, so the browser path cannot silently rot.

index.html is the development shell; producing a distributable bundle needs wasm-pack and is left out of this PR.