When running under XWayland (Wayland sessions with GDK_BACKEND=x11),
WebKit2GTK's compositing mode can fail silently, causing the Setup
Wizard WebView to freeze or render blank. This leaves users stuck on
the "Loading......" screen indefinitely.
Changes:
- Set WEBKIT_DISABLE_COMPOSITING_MODE=1 to force software rendering,
matching the fix used by BambuStudio
- Enable the 20-second timeout fallback in load.js so the wizard
proceeds even if the C++ -> JavaScript signal fails
