Add NVIDIA stress loader selection and DCGM 4 support

iso/overlay/usr/local/bin/bee-nvidia-load

@@ -114,4 +114,19 @@ fi
 ldconfig 2>/dev/null || true
 log "ldconfig refreshed"
 
+# Start DCGM host engine so dcgmi can discover GPUs.
+# nv-hostengine must run before any dcgmi command — without it, dcgmi reports
+# "group is empty" even when GPUs and modules are present.
+# Skip if already running (e.g. started by a dcgm systemd service or prior boot).
+if command -v nv-hostengine >/dev/null 2>&1; then
+    if pgrep -x nv-hostengine >/dev/null 2>&1; then
+        log "nv-hostengine already running — skipping"
+    else
+        nv-hostengine
+        log "nv-hostengine started"
+    fi
+else
+    log "WARN: nv-hostengine not found — dcgmi diagnostics will not work"
+fi
+
 log "done"