Server-side headless PNG rendering (kept out-of-tree) #36

Problem

There is no way to turn a saved document (store.getSnapshot()) into a PNG on a Node.js server without launching a browser (Chromium/Puppeteer/Playwright). Any backend that renders, prints, archives or thumbnails boards server-side needs this.

Proposed solution — kept out of this repo

A working implementation lives separately at https://github.com/calumk/quickdrawjs-headless: renderPng(snapshot, { width, height, theme, background, fit, viewport, padding }) returns a PNG Buffer, reusing the core drawShape engine over a native Skia canvas. No browser globals, no automation; 25 tests, docs and a realistic example included.

It is deliberately not proposed as a packages/* addition here: rendering on Skia means shipping native prebuilt-binary dependencies (the Skia engine binaries, BSD-3, via the MIT-licensed skia-canvas wrapper) plus a platform support matrix that this dependency-free core package should not carry.
The chain is permissive (MIT / BSD-3 / OFL), but not MIT.

If it is deemed useful (similar to the react package) let me know, and I can open a PR to move it back to packages.

Why im raising an issue -

To support this, we need a small change to the core.

A tiny, dependency-free seam (no behavior change) - See the PR