Doobie v0.13.5

Fixed (Linux)

• Restored GPU compositing on Linux. v0.13.3/v0.13.4 unconditionally
  set WEBKIT_DISABLE_DMABUF_RENDERER=1 and
  WEBKIT_DISABLE_COMPOSITING_MODE=1 as a blanket fix for the
  NVIDIA-proprietary-Wayland white-window class. That worked, but it
  also turned off GPU compositing for everyone else -- a user on
  Ubuntu 26.04 + Intel iGPU reported 1 fps in Ardour because of
  this. Both env vars removed from the defaults. Only GDK_BACKEND=x11
  stays (correctness fix -- JUCE's WebKit child is an X11 client). The
  README now documents these env vars as opt-in workarounds for users
  who actually hit the NVIDIA-Wayland white window.