Removes extension/, desktop-client/backends/, desktop-client/config.js,
server/, root package.json/package-lock.json/node_modules/, and the
now-unused electron-store dependency from desktop-client/package.json.
The desktop-client is now a self-contained Electron app with no external
deps beyond express and ws.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>