fix(grafana): restore datasources and GPU power metric

Assisted-by: DeepSeek Harness (deepseek-flash)

hosts/12kingdoms-youko/homelab-services/grafana/dashboards/homelab/gpu.json

@@ -178,7 +178,7 @@
         "type": "prometheus",
         "uid": "${DS_PROMETHEUS}"
       },
-      "description": "node_hwmon_power_watt / node_hwmon_temp_celsius for the amdgpu chip",
+      "description": "node_hwmon_power_average_watt / node_hwmon_temp_celsius for the amdgpu chip",
       "fieldConfig": {
         "defaults": {
           "color": {
@@ -242,7 +242,7 @@
             "type": "prometheus",
             "uid": "${DS_PROMETHEUS}"
           },
-          "expr": "node_hwmon_power_watt{host=\"$host\", chip=~\"$chip\"}",
+          "expr": "node_hwmon_power_average_watt{host=\"$host\", chip=~\"$chip\"}",
           "legendFormat": "power",
           "refId": "A"
         },

hosts/12kingdoms-youko/homelab-services/grafana/default.nix

@@ -49,6 +49,12 @@
 
     # https://github.com/NixOS/nixpkgs/tree/master/pkgs/servers/monitoring/grafana/plugins
     declarativePlugins = with pkgs.grafanaPlugins; [
+      # Grafana 13 moved the built-in Prometheus/Loki datasources out of the
+      # server package; provision them explicitly so existing datasources and
+      # dashboards keep working.
+      prometheus
+      loki
+
       # https://github.com/VictoriaMetrics/victoriametrics-datasource
       # supports victoria-metrics's MetricsQL, template, tracing, prettify, etc.
       victoriametrics-metrics-datasource