Improve Node.js/browser environment detection and dependency handling

- Updated shims.js to properly detect Node.js vs browser environments
- Only attempt to require Node.js modules (ws/jsdom) when actually in Node.js
- Added clearer error messages explaining required packages
- Moved jsdom and ws from optionalDependencies to peerDependencies
- Updated README.md to document Node.js requirements
- Added peerDependenciesMeta to mark Node.js deps as optional
- Improved error messages to be more specific about environment requirements

Author: jcbrand

.gitignore

@@ -16,3 +16,4 @@ doc
 doc-tmp
 tags.lock
 tags.temp
+.aider*

README.md

@@ -26,6 +26,16 @@ Mobile Safari, Chrome, Chrome for Android, Opera and the mobile Opera browser.
 
 Since version 1.3.0, support for IE < 11 has been dropped.
 
+### Node.js
+
+When running in Node.js, you'll need to install these additional packages:
+
+```bash
+npm install jsdom ws
+```
+
+These provide the required WebSocket and DOM APIs that are normally available in browsers.
+
 ### React Native
 
 Since version 1.6.0 the [WebCrypto](https://developer.mozilla.org/en-US/docs/Web/API/Web_Crypto_API)