Fix blank screen / Crash on Linux due to Wayland, NVIDIA, etc

Possible error messages:

• Error 71 (Protocol error) dispatching to Wayland display

• Cannot create EGL context: invalid display

If Yaak crashes or shows a blank screen on Linux, try setting one of the following environment variables:

• WEBKIT_DISABLE_COMPOSITING_MODE=1 forces accelerated compositing off in WebKitGTK.

• WEBKIT_DISABLE_DMABUF_RENDERER=1 disables the newer DMA-BUF renderer, which is the default in recent WebKitGTK and is generally the right path—except it’s been flaky with NVIDIA proprietary drivers(white/blank screens, flicker).

• __NV_DISABLE_EXPLICIT_SYNC=1 makes the driver / EGL-Wayland layer turn off or ignore the explicit sync path and fall back to older (less strict) synchronization paths