The daemon is a detached process that survives Electron restarts,
so after an auto-update the old daemon version would keep running.
Now we stop it before quitAndInstall so the new app instance
starts a fresh daemon with the updated binary.
Downloads and loads React DevTools Chrome extension using Electron 41's
session.extensions API directly, avoiding the deprecated session.loadExtension
used by electron-devtools-installer. Extension is cached in userData after
first download. Only loaded when !app.isPackaged.