Upgrade Node.js from 18 to 20 across build, test, website and repo

- Update .nvmrc from 18.20.8 to 20.19.0 (Node 20 LTS)
- Update package.json engines field from >=14 to >=18
- Update CONTRIBUTING.md to document >=20 requirement
- Update Dockerfile base image from node:8.9.0 to node:20

CI workflows already use node-version-file: '.nvmrc' so they
will automatically pick up the new Node 20 version.

https://claude.ai/code/session_016oyFSyGm7hYU1e1KDXqjnW

Author: claude

.nvmrc

@@ -1 +1 @@
-18.20.8
+20.19.0

CONTRIBUTING.md

@@ -9,7 +9,7 @@ PRs and bug reports are welcome, and we are actively looking for new maintainers
 
 The **master** branch is the active development branch.
 
-Building deck.gl locally from the source requires node.js `>=18`. Further limitations on the Node version may be imposed by [puppeteer](https://github.com/puppeteer/puppeteer#usage) and [headless-gl](https://github.com/stackgl/headless-gl#supported-platforms-and-nodejs-versions).
+Building deck.gl locally from the source requires node.js `>=20`. Further limitations on the Node version may be imposed by [puppeteer](https://github.com/puppeteer/puppeteer#usage) and [headless-gl](https://github.com/stackgl/headless-gl#supported-platforms-and-nodejs-versions).
 We use [yarn](https://yarnpkg.com/en/docs/install) to manage the dependencies of deck.gl. The project's automated builds use Node [corepack](https://github.com/nodejs/corepack) to manage the yarn version. For local development, you can use [nvm](https://github.com/nvm-sh/nvm) or any other Node version manager of your choice - a `.nvmrc` configuration file is provided.
 
 ```bash

Dockerfile

@@ -1,4 +1,4 @@
-FROM node:8.9.0
+FROM node:20
 
 WORKDIR /deck-gl
 ENV PATH /deck-gl/node_modules/.bin:$PATH

package.json

@@ -63,7 +63,7 @@
     "bindings-precommit-tests"
   ],
   "engines": {
-    "node": ">=14"
+    "node": ">=18"
   },
   "packageManager": "yarn@1.22.19"
 }