grafana: switch the CLAUDE.md-size panel from a snapshot bar to a time series

mara, PR review: "i want to see it over time - sounds like you built
bar chart?" — correct, it was a bargauge (instant/lastNotNull). Switched
to timeseries, matching the CPU/memory-by-agent panels' own treatment of
a plain live gauge (raw value plotted across the range, no rate()/
increase() since it's not a cumulative counter).

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

@@ -658,6 +658,63 @@
           "values": false
         }
       }
+    },
+    {
+      "id": 33,
+      "type": "timeseries",
+      "title": "CLAUDE.md size by agent",
+      "description": "hyperhive.agent.claude_md.lines over time — mara: \"i want to see it over time\" (a bargauge snapshot in an earlier round of this panel only showed the current count). A continuously-live gauge, not a per-turn counter, so this is the raw value plotted across the range, same treatment as the CPU/memory-by-agent panels above rather than a rate()/increase(). The harness itself raises a loose-ends todo past 500 lines suggesting a trim, not a hard limit — this panel is visibility, not an alarm.",
+      "datasource": {
+        "type": "prometheus",
+        "uid": "@datasourceUid@"
+      },
+      "gridPos": {
+        "h": 8,
+        "w": 12,
+        "x": 0,
+        "y": 27
+      },
+      "targets": [
+        {
+          "refId": "A",
+          "datasource": {
+            "type": "prometheus",
+            "uid": "@datasourceUid@"
+          },
+          "expr": "sum by (agent) ({__name__=\"hyperhive.agent.claude_md.lines\", hive=~\"$hive\", agent=~\"$agent\"})",
+          "legendFormat": "{{agent}}"
+        }
+      ],
+      "fieldConfig": {
+        "defaults": {
+          "unit": "short",
+          "decimals": 0,
+          "color": {
+            "mode": "palette-classic"
+          },
+          "custom": {
+            "drawStyle": "line",
+            "lineWidth": 1,
+            "fillOpacity": 0,
+            "showPoints": "never",
+            "spanNulls": false,
+            "axisSoftMin": 0
+          }
+        },
+        "overrides": []
+      },
+      "options": {
+        "legend": {
+          "displayMode": "list",
+          "placement": "bottom",
+          "showLegend": true,
+          "calcs": []
+        },
+        "tooltip": {
+          "mode": "multi",
+          "sort": "desc"
+        }
+      }
     }
   ]
 }