fix: use showLegend false for hidden timeseries legends

displayMode: hidden ist in dieser Grafana-Version fuer Timeseries ungueltig
und liess die Panels (Solarstrahlung, Luftdruck, Wallbox-Ladeleistung) leer.
Auf legend.showLegend=false umgestellt.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

monitoring/grafana/dashboards/solar-pv.json

@@ -167,7 +167,7 @@
       "gridPos": { "h": 7, "w": 12, "x": 0, "y": 30 },
       "datasource": { "type": "influxdb", "uid": "ha-weather-influx" },
       "fieldConfig": { "defaults": { "unit": "kwatt", "color": { "mode": "fixed", "fixedColor": "#9775fa" }, "custom": { "drawStyle": "line", "fillOpacity": 20, "lineWidth": 2 } }, "overrides": [] },
-      "options": { "legend": { "displayMode": "hidden" }, "tooltip": { "mode": "single" } },
+      "options": { "legend": { "showLegend": false }, "tooltip": { "mode": "single" } },
       "targets": [ { "refId": "A", "datasource": { "type": "influxdb", "uid": "ha-weather-influx" }, "rawQuery": true, "format": "time_series", "rawSql": "SELECT time, value FROM \"kW\" WHERE entity_id = 'eh7klptt_leistung' AND $__timeFilter(time) ORDER BY time" } ]
     },
     {