swarm-grafana: add cost/tokens-by-agent panels to the claude usage dashboard

The dashboard already templated an $agent variable and broke turns and
active-time out by agent, but cost and token totals only split by
model, effort and query_source -- there was no panel answering "how
much did each agent spend/use", the aggregate-by-agent view mara asked
for.

nix/host-modules/swarm-grafana/dashboards/claude-usage.json

@@ -5,7 +5,7 @@
   "tags": ["hyperhive", "claude"],
   "timezone": "utc",
   "schemaVersion": 39,
-  "version": 1,
+  "version": 2,
   "editable": true,
   "refresh": "1m",
   "time": {
@@ -874,6 +874,124 @@
           "values": false
         }
       }
+    },
+    {
+      "id": 42,
+      "type": "bargauge",
+      "title": "Cost by agent",
+      "description": "claude_code.cost.usage summed over the selected range, broken out by agent — which agent the spend belongs to, as opposed to the model/effort/source breakdowns above.",
+      "datasource": {
+        "type": "prometheus",
+        "uid": "@datasourceUid@"
+      },
+      "gridPos": {
+        "h": 7,
+        "w": 12,
+        "x": 0,
+        "y": 32
+      },
+      "targets": [
+        {
+          "refId": "A",
+          "datasource": {
+            "type": "prometheus",
+            "uid": "@datasourceUid@"
+          },
+          "expr": "sum by (agent) (increase({__name__=\"claude_code.cost.usage\", hive=~\"$hive\", agent=~\"$agent\"}[$__range]))",
+          "instant": true,
+          "legendFormat": "{{agent}}"
+        }
+      ],
+      "fieldConfig": {
+        "defaults": {
+          "unit": "currencyUSD",
+          "decimals": 2,
+          "color": {
+            "mode": "fixed",
+            "fixedColor": "purple"
+          },
+          "thresholds": {
+            "mode": "absolute",
+            "steps": [
+              {
+                "color": "purple",
+                "value": null
+              }
+            ]
+          }
+        },
+        "overrides": []
+      },
+      "options": {
+        "displayMode": "basic",
+        "orientation": "horizontal",
+        "showUnfilled": true,
+        "valueMode": "text",
+        "reduceOptions": {
+          "calcs": ["lastNotNull"],
+          "fields": "",
+          "values": false
+        }
+      }
+    },
+    {
+      "id": 43,
+      "type": "bargauge",
+      "title": "Tokens by agent",
+      "description": "claude_code.token.usage summed over the selected range, broken out by agent (all token types combined).",
+      "datasource": {
+        "type": "prometheus",
+        "uid": "@datasourceUid@"
+      },
+      "gridPos": {
+        "h": 7,
+        "w": 12,
+        "x": 12,
+        "y": 32
+      },
+      "targets": [
+        {
+          "refId": "A",
+          "datasource": {
+            "type": "prometheus",
+            "uid": "@datasourceUid@"
+          },
+          "expr": "sum by (agent) (increase({__name__=\"claude_code.token.usage\", hive=~\"$hive\", agent=~\"$agent\"}[$__range]))",
+          "instant": true,
+          "legendFormat": "{{agent}}"
+        }
+      ],
+      "fieldConfig": {
+        "defaults": {
+          "unit": "short",
+          "decimals": 0,
+          "color": {
+            "mode": "fixed",
+            "fixedColor": "blue"
+          },
+          "thresholds": {
+            "mode": "absolute",
+            "steps": [
+              {
+                "color": "blue",
+                "value": null
+              }
+            ]
+          }
+        },
+        "overrides": []
+      },
+      "options": {
+        "displayMode": "basic",
+        "orientation": "horizontal",
+        "showUnfilled": true,
+        "valueMode": "text",
+        "reduceOptions": {
+          "calcs": ["lastNotNull"],
+          "fields": "",
+          "values": false
+        }
+      }
     }
   ]
 }