udev: match kfd by name only — misc-class devices have no udev subsystem

The first revision guarded the kfd line with SUBSYSTEM=="misc", which never
matches (misc-class devices carry no subsystem for udev matching), so the rule
was read but never fired and /dev/kfd stayed 0660 root:render. Name-only match
applies 0666 on creation and on trigger.

Also fixes test-changed.sh to exit 0 when changed paths map to zero tests
(udev rules are mapped-but-untestable) instead of invoking bats with an empty
selection.

dankclaw/udev/99-comfyui-gpu-access.rules

@@ -15,7 +15,7 @@
 # domain) can already ptrace the GPU userspace through an existing holder's
 # fd inheritance; on a private single-administrator home server this trades a
 # capability gate that could never be held by the intended user anyway.
-# Render nodes and /dev/kfd are compute nodes only — display outputs (card0,
-# card1) keep their owner/group/mode.
-KERNEL=="kfd", SUBSYSTEM=="misc", MODE="0666"
+# Note the missing SUBSYSTEM= guard on the kfd line: misc-class devices have no
+# subsystem for udev matching, so a SUBSYSTEM=="misc" guard never matches.
+KERNEL=="kfd", MODE="0666"
 KERNEL=="renderD*", SUBSYSTEM=="drm", MODE="0666"