metrics: phase 3 straylight/rift scrapes and hyperborea units

Review, no switch. node-laptop for talos/titan is excluded from
FleetTargetDown. llama-straylight scrape uses params.model for
ornith-1.5-35b-a3b (router 400 without it; will load if cold).

configs/metrics/hyperborea/override.conf

@@ -0,0 +1,7 @@
+# /etc/systemd/system/prometheus-node-exporter.service.d/override.conf
+[Unit]
+After=tailscaled.service
+Wants=tailscaled.service
+
+[Service]
+Restart=on-failure

configs/metrics/hyperborea/prometheus-node-exporter

@@ -0,0 +1,3 @@
+# /etc/default/prometheus-node-exporter on hyperborea (Debian).
+# Bind the tailscale IP only. LAN 192.168.88.154:9100 must stay closed.
+ARGS="--web.listen-address=100.112.40.10:9100"

configs/metrics/straylight.nix

@@ -0,0 +1,45 @@
+# Straylight node_exporter extras: amdgpu hwmon/DRM plus GTT textfile gauges.
+{ pkgs, ... }:
+{
+  imports = [ ./exporters.nix ];
+
+  services.prometheus.exporters.node = {
+    enabledCollectors = [ "hwmon" "drm" "textfile" ];
+    extraFlags = [
+      "--collector.textfile.directory=/var/lib/prometheus-node-exporter"
+    ];
+  };
+
+  systemd.tmpfiles.rules = [
+    "d /var/lib/prometheus-node-exporter 0755 root root -"
+  ];
+
+  systemd.services.node-exporter-gtt = {
+    description = "Write AMD GTT gauges for node_exporter textfile";
+    serviceConfig.Type = "oneshot";
+    script = ''
+      set -eu
+      d=/var/lib/prometheus-node-exporter
+      total=$(${pkgs.coreutils}/bin/cat /sys/class/drm/card1/device/mem_info_gtt_total)
+      used=$(${pkgs.coreutils}/bin/cat /sys/class/drm/card1/device/mem_info_gtt_used)
+      tmp="$d/gtt.prom.$$"
+      ${pkgs.coreutils}/bin/printf '%s\n' \
+        '# HELP gtt_total_bytes AMD GTT size in bytes' \
+        '# TYPE gtt_total_bytes gauge' \
+        "gtt_total_bytes $total" \
+        '# HELP gtt_used_bytes AMD GTT used in bytes' \
+        '# TYPE gtt_used_bytes gauge' \
+        "gtt_used_bytes $used" > "$tmp"
+      ${pkgs.coreutils}/bin/mv "$tmp" "$d/gtt.prom"
+    '';
+  };
+
+  systemd.timers.node-exporter-gtt = {
+    wantedBy = [ "timers.target" ];
+    timerConfig = {
+      OnBootSec = "15s";
+      OnUnitActiveSec = "15s";
+      AccuracySec = "1s";
+    };
+  };
+}