feat(demo): Prometheus + Grafana with a provisioned dashboard

make demo-ui now also starts Prometheus (scrapes coordinator:8080/metrics) and
Grafana with a provisioned datasource and a SciMesh Coordinator dashboard
(request rate & p95 by route, status mix, goroutines, RSS). Grafana allows
anonymous viewing so the dashboard opens without a login; admin/admin to edit.

- monitoring/prometheus.yml + grafana provisioning + dashboard JSON
- docker-compose.monitoring.yml overlay (third -f in demo-ui.sh)
- demo prints the Grafana and Prometheus URLs

coordinator/monitoring/grafana/dashboards/coordinator.json

@@ -0,0 +1,88 @@
+{
+  "annotations": { "list": [] },
+  "editable": true,
+  "graphTooltip": 1,
+  "schemaVersion": 39,
+  "tags": ["scimesh"],
+  "time": { "from": "now-15m", "to": "now" },
+  "refresh": "5s",
+  "title": "SciMesh Coordinator",
+  "uid": "scimesh-coordinator",
+  "panels": [
+    {
+      "type": "timeseries",
+      "title": "HTTP request rate by route",
+      "datasource": { "type": "prometheus", "uid": "prometheus" },
+      "gridPos": { "h": 8, "w": 12, "x": 0, "y": 0 },
+      "fieldConfig": { "defaults": { "unit": "reqps" }, "overrides": [] },
+      "targets": [
+        {
+          "refId": "A",
+          "datasource": { "type": "prometheus", "uid": "prometheus" },
+          "expr": "sum by (route) (rate(scimesh_http_requests_total[1m]))",
+          "legendFormat": "{{route}}"
+        }
+      ]
+    },
+    {
+      "type": "timeseries",
+      "title": "p95 latency by route",
+      "datasource": { "type": "prometheus", "uid": "prometheus" },
+      "gridPos": { "h": 8, "w": 12, "x": 12, "y": 0 },
+      "fieldConfig": { "defaults": { "unit": "s" }, "overrides": [] },
+      "targets": [
+        {
+          "refId": "A",
+          "datasource": { "type": "prometheus", "uid": "prometheus" },
+          "expr": "histogram_quantile(0.95, sum by (le, route) (rate(scimesh_http_request_duration_seconds_bucket[5m])))",
+          "legendFormat": "{{route}}"
+        }
+      ]
+    },
+    {
+      "type": "timeseries",
+      "title": "Requests by status",
+      "datasource": { "type": "prometheus", "uid": "prometheus" },
+      "gridPos": { "h": 8, "w": 12, "x": 0, "y": 8 },
+      "fieldConfig": { "defaults": { "unit": "reqps" }, "overrides": [] },
+      "targets": [
+        {
+          "refId": "A",
+          "datasource": { "type": "prometheus", "uid": "prometheus" },
+          "expr": "sum by (status) (rate(scimesh_http_requests_total[1m]))",
+          "legendFormat": "{{status}}"
+        }
+      ]
+    },
+    {
+      "type": "timeseries",
+      "title": "Goroutines",
+      "datasource": { "type": "prometheus", "uid": "prometheus" },
+      "gridPos": { "h": 8, "w": 6, "x": 12, "y": 8 },
+      "fieldConfig": { "defaults": { "unit": "short" }, "overrides": [] },
+      "targets": [
+        {
+          "refId": "A",
+          "datasource": { "type": "prometheus", "uid": "prometheus" },
+          "expr": "go_goroutines{job=\"coordinator\"}",
+          "legendFormat": "goroutines"
+        }
+      ]
+    },
+    {
+      "type": "timeseries",
+      "title": "Resident memory",
+      "datasource": { "type": "prometheus", "uid": "prometheus" },
+      "gridPos": { "h": 8, "w": 6, "x": 18, "y": 8 },
+      "fieldConfig": { "defaults": { "unit": "bytes" }, "overrides": [] },
+      "targets": [
+        {
+          "refId": "A",
+          "datasource": { "type": "prometheus", "uid": "prometheus" },
+          "expr": "process_resident_memory_bytes{job=\"coordinator\"}",
+          "legendFormat": "rss"
+        }
+      ]
+    }
+  ]
+}

coordinator/monitoring/grafana/provisioning/dashboards/provider.yml

@@ -0,0 +1,10 @@
+apiVersion: 1
+
+providers:
+  - name: SciMesh
+    type: file
+    disableDeletion: false
+    allowUiUpdates: true
+    options:
+      path: /var/lib/grafana/dashboards
+      foldersFromFilesStructure: false

coordinator/monitoring/grafana/provisioning/datasources/prometheus.yml

@@ -0,0 +1,10 @@
+apiVersion: 1
+
+datasources:
+  - name: Prometheus
+    uid: prometheus
+    type: prometheus
+    access: proxy
+    url: http://prometheus:9090
+    isDefault: true
+    editable: false

coordinator/monitoring/prometheus.yml

@@ -0,0 +1,10 @@
+# Prometheus scrape config for the SciMesh demo. Prometheus runs in the same
+# compose network as the coordinator, so it reaches it by service name.
+global:
+  scrape_interval: 5s
+  evaluation_interval: 5s
+
+scrape_configs:
+  - job_name: coordinator
+    static_configs:
+      - targets: ["coordinator:8080"]