Add nodejs: WebAssembly Node package with no native dependency

New nodejs/ package: a wasm-bindgen crate (vtracer-wasm) built with wasm-pack
that wraps the vtracer framework, plus a thin JS layer for file I/O. Image
decoding (png/jpeg/gif/bmp via the image crate) runs in wasm too, so the
package has zero native dependencies — no sharp, no node-gyp.

No separate general-purpose wasm crate: the Node package directly owns and
wraps the wasm. Excluded from the cargo workspace (wasm-bindgen cdylib), built
with wasm-pack.

JS API (camelCase options): convertBuffer, convertPixels, convertFile,
convertFileSync — each taking an Options object (preset, colorMode,
hierarchical/cutout mosaic, mode, palette, maxColors, optimize, ...). Ships
index.d.ts types and a node smoke test. README updated.

Verified: builds to wasm32-unknown-unknown; `node test.js` passes; output
matches the CLI/Python bindings (253 paths on the tank sample).

README.md

@@ -146,6 +146,22 @@ vtracer.Config.poster().convert_file("photo.jpg", "poster.svg")
 
 See [`crates/vtracer-py`](crates/vtracer-py/README.md) for the full API.
 
+### Node.js Library
+
+[`vtracer`](https://www.npmjs.com/package/vtracer) is available for Node as a WebAssembly build (from the [`nodejs`](nodejs/README.md) package) — image decoding and vectorization both run in wasm, so there is **no native dependency**.
+
+```sh
+npm install vtracer
+```
+
+```js
+const vtracer = require('vtracer');
+
+await vtracer.convertFile('in.png', 'out.svg', { mode: 'polygon' });
+const svg = vtracer.convertBuffer(buffer, { preset: 'poster' });
+const svg2 = vtracer.convertPixels(rgba, width, height, { colorMode: 'bw' });
+```
+
 ## Citations
 
 VTracer has since been cited by a few academic papers in computer graphics / vision research. Please kindly let us know if you have cited our work: