swarm-grafana: sort multi-series bargauge panels by value

Bargauge panels display series in the order the datasource returns them —
Grafana has no native sort for that (long-standing upstream gap, grafana#17245).
The reliable fix is sorting at the PromQL level with sort_desc() on an
instant vector, which forge.json's 'Issues by label' panel already does.
Applies the same pattern to the other 14 multi-series bargauge panels across
agents.json, claude-usage.json, and authelia.json (the latter two also
needed instant: true added, since sort_desc only works on instant vectors).

logstore.json's two VictoriaLogs-backed bargauge panels use LogsQL, not
PromQL, and are left out of this pass — LogsQL's sort-after-stats has a
documented ordering bug in some versions; needs its own verification.

nix/host-modules/swarm-grafana/dashboards/authelia.json

@@ -255,7 +255,8 @@
             "type": "prometheus",
             "uid": "@datasourceUid@"
           },
-          "expr": "sum by (code) (increase(authelia_request[$__range]))",
+          "expr": "sort_desc(sum by (code) (increase(authelia_request[$__range])))",
+          "instant": true,
           "legendFormat": "{{code}}"
         }
       ],
@@ -302,7 +303,8 @@
             "type": "prometheus",
             "uid": "@datasourceUid@"
           },
-          "expr": "sum by (code) (increase(authelia_authz[$__range]))",
+          "expr": "sort_desc(sum by (code) (increase(authelia_authz[$__range])))",
+          "instant": true,
           "legendFormat": "{{code}}"
         }
       ],