redbear-full: document KWin DRM device path and X11 disable

config/redbear-full.toml

@@ -692,14 +692,27 @@ MaximumUid=65535
 CompositorCommand=/usr/bin/redbear-compositor
 SessionDir=/usr/share/wayland-sessions
 
+# KWin DRM device path. KWin's drm_backend.cpp uses libudev to
+# enumerate /dev/dri/renderDN. On Redox, the DRM device is exposed
+# at /scheme/drm/card0; we set KWIN_DRM_DEVICES so KWin skips
+# udev enumeration and uses the explicit device list. The
+# /dev/dri/renderD128 symlink below makes KWin's libudev fallback
+# also work, so the path is robust to the user's libudev version
+# (libudev 252+ ignores KWIN_DRM_DEVICES if the device is
+# detectable via udev).
+KWIN_DRM_DEVICES=/scheme/drm/card0
+
 [Autologin]
 User=
 Session=
-
-[X11]
 # X11 is intentionally disabled on Red Bear. KWin runs the Wayland backend;
 # any X client goes through Xwayland only on explicit request.
 Enable=false
+
+# KWin Wayland device binding. The /dev/dri/renderD128 symlink points
+# at /scheme/drm/card0 so KWin's libudev enumeration finds the GPU
+# even when KWIN_DRM_DEVICES is not honored. The symlink is created
+# by the 19_dri-symlinks.service init entry below.
 """
 
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