The component uses className="app-body" but CSS targeted .main for the grid layout.
This caused leftbar, canvas, and rightbar to all render at full viewport width
instead of the 3-column grid (leftbar 64px | canvas 1fr | rightbar 240px).
- Change DEFAULT_WS_URL from ws://hostname:3001 to wss://window.location.host
- Wrap WebSocket constructor in try/catch to prevent React crash on connection error
- Fixes white page when opening a project (CADEditor crashed on insecure ws:// from HTTPS page)