P1: When Node.js is missing, auto-install via brew (macOS) or winget (Windows)
instead of stopping and asking user to install manually.
P1: Auto-open install wizard on first disconnect detection in Electron,
with localStorage flag to avoid re-prompting after dismissal.
P2: IPC install:start now throws on concurrent calls instead of returning
silent { error } object. Removed unused return values from handlers.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>