fix: create /dev/nvidia* nodes in bee-nvidia — mdev has no NVIDIA rules

Alpine uses mdev which has no rules for NVIDIA devices. Without /dev/nvidiactl
and /dev/nvidia{0-7}, nvidia-smi returns NVML_ERROR_LIBRARY_NOT_FOUND (exit 12)
even though kernel modules are loaded and libraries are present.

Fix: after insmod, read major numbers from /proc/devices and mknod the required
character devices (/dev/nvidiactl, /dev/nvidia{0-7}, /dev/nvidia-uvm).

Add /dev/nvidia* node checks to smoketest for earlier failure detection.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

iso/builder/smoketest.sh

@@ -62,6 +62,16 @@ for mod in nvidia nvidia_modeset nvidia_uvm; do
     fi
 done
 
+echo ""
+echo "-- NVIDIA device nodes --"
+for dev in nvidiactl nvidia0 nvidia-uvm; do
+    if [ -e "/dev/$dev" ]; then
+        ok "/dev/$dev exists"
+    else
+        fail "/dev/$dev missing — nvidia-smi will return NVML_ERROR_LIBRARY_NOT_FOUND"
+    fi
+done
+
 echo ""
 echo "-- nvidia-smi --"
 if PATH="/usr/local/bin:$PATH" command -v nvidia-smi >/dev/null 2>&1; then