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/node-red.yaml

@@ -0,0 +1,16 @@
+name: node-red
+version: "1.0.0"
+description: Node-RED MCP server for flow management and automation
+packageName: "mcp-node-red"
+transport: STDIO
+repositoryUrl: https://github.com/fx/mcp-node-red
+healthCheck:
+  tool: get_settings
+  arguments: {}
+env:
+  - name: NODE_RED_URL
+    description: Node-RED instance URL (e.g. http://nodered.local:1880)
+    required: true
+  - name: NODE_RED_TOKEN
+    description: Node-RED access token (optional if no auth)
+    required: false