feat: add MCP healthcheck probes and new templates (grafana, home-assistant, node-red)

- Add healthCheck spec to templates and servers (tool, arguments, interval, timeout, failureThreshold)
- Add healthStatus, lastHealthCheck, events fields to instances
- Create grafana, home-assistant, node-red templates with healthcheck probes
- Add healthcheck probes to existing templates (github, slack, postgres, jira)
- Show HEALTH column in `get instances` and Events section in `describe instance`
- Display healthCheck details in `describe server` and `describe template`
- Schema + storage + display only; actual probe runner is future work

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

templates/grafana.yaml

@@ -0,0 +1,16 @@
+name: grafana
+version: "1.0.0"
+description: Grafana MCP server for dashboards, datasources, and alerts
+packageName: "@leval/mcp-grafana"
+transport: STDIO
+repositoryUrl: https://github.com/levalhq/mcp-grafana
+healthCheck:
+  tool: list_datasources
+  arguments: {}
+env:
+  - name: GRAFANA_URL
+    description: Grafana instance URL (e.g. https://grafana.example.com)
+    required: true
+  - name: GRAFANA_SERVICE_ACCOUNT_TOKEN
+    description: Grafana service account token (glsa_...)
+    required: true