Node.js: add ESM support (dual CJS + ESM build)

[kalwalt]

Summary

Add ESM consumption for the experimental Node.js build so named imports work:

import { ARControllerNFT, ARToolkitNFT } from '@webarkit/jsartoolkit-nft';

Today the Node build is commonjs2 only, so consumers must use require() or a default import (Node can't statically read named exports from the CJS bundle). This is the top capability gap for the Node support.

Proposed approach — dual CJS + ESM (non-breaking)

• Keep the existing dist/ARToolkitNFT_node.js (CommonJS).
• Add a separate ESM bundle, e.g. dist/ARToolkitNFT_node.mjs, via a webpack target with output.library.type: "module" + experiments.outputModule: true (and target: "node").
• Wire package.json exports so the Node entry serves both:

  "node": {
    "import": { "types": "./types/src/index_node.d.ts", "default": "./dist/ARToolkitNFT_node.mjs" },
    "require": { "types": "./types/src/index_node.d.ts", "default": "./dist/ARToolkitNFT_node.js" }
  }

• main and the existing require() path stay unchanged → no breaking change.

Alternatives considered

• ESM-only node build — cleaner single artifact, but breaks existing require() consumers. Rejected.

Tasks

• Add ESM webpack target for the node entry (output.library.type: "module").
• Update tools/makem.js if a different wasm flavor is needed for ESM (verify the existing _node_wasm glue works under ESM).
• Add import/require conditions to the exports map.
• Add/verify an ESM example (example.mjs) using import { ARControllerNFT }.
• Update README Node.js section (the "named import not yet supported" caveat).

Notes

• Experimental Node.js support — see Feature node libs #140. Work targets the dev branch.
• Verify with npm run build-ts + a runnable ESM example before release.