feat(helm): Add observability support with ServiceMonitor and Grafana dashboard

Add comprehensive observability configuration to Helm chart:

**Helm Values:**
- Add observability configuration section for metrics, tracing, and logging
- Add serviceMonitor configuration (disabled by default)
- Add prometheusRule configuration (disabled by default)

**Templates:**
- Update deployment to include observability environment variables
- Update deployment to expose metrics port (9090)
- Update service to expose metrics port
- Add ServiceMonitor template for Prometheus Operator
- Add PrometheusRule template with critical and warning alerts

**Dashboards:**
- Add comprehensive Grafana dashboard JSON with 6 panels:
  - Request Rate (by method and endpoint)
  - Error Rate (5xx errors percentage)
  - Request Latency (P50/P95 by endpoint)
  - Top MCP Tools (by invocation volume)
  - Nextcloud API Latency (by app)
  - Vector Sync Queue Size
- Add dashboard README with import instructions

**Alert Rules:**
- Critical: Server down, high error rate (>5%), high latency (>1s), dependency down
- Warning: Token validation errors (>1%), vector sync queue high (>100), Qdrant slow (>500ms)

All features are opt-in via values.yaml configuration.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

charts/nextcloud-mcp-server/dashboards/README.md

@@ -0,0 +1,90 @@
+# Grafana Dashboards
+
+This directory contains example Grafana dashboards for monitoring the Nextcloud MCP Server.
+
+## Dashboards
+
+### nextcloud-mcp-server.json
+
+Comprehensive dashboard with the following panels:
+
+- **Request Rate**: HTTP requests per second by method and endpoint
+- **Error Rate**: Percentage of 5xx errors
+- **Request Latency**: P50 and P95 latency by endpoint
+- **Top MCP Tools**: Most frequently called tools
+- **Nextcloud API Latency**: API call latency by app (notes, calendar, etc.)
+- **Vector Sync Queue**: Queue size for background document processing
+
+## Importing to Grafana
+
+### Manual Import
+
+1. Open Grafana UI
+2. Navigate to Dashboards → Import
+3. Upload `nextcloud-mcp-server.json`
+4. Select your Prometheus data source
+5. Click "Import"
+
+### Automated Import (Kubernetes)
+
+If using the Grafana Operator or kube-prometheus-stack, you can create a ConfigMap:
+
+```bash
+kubectl create configmap nextcloud-mcp-dashboards \
+  --from-file=nextcloud-mcp-server.json \
+  -n monitoring
+
+# Add label for Grafana sidecar to discover
+kubectl label configmap nextcloud-mcp-dashboards \
+  grafana_dashboard=1 \
+  -n monitoring
+```
+
+Or add to your Helm values:
+
+```yaml
+# values.yaml for kube-prometheus-stack
+grafana:
+  dashboardProviders:
+    dashboardproviders.yaml:
+      apiVersion: 1
+      providers:
+        - name: 'nextcloud-mcp'
+          orgId: 1
+          folder: 'Nextcloud MCP'
+          type: file
+          disableDeletion: false
+          editable: true
+          options:
+            path: /var/lib/grafana/dashboards/nextcloud-mcp
+
+  dashboardsConfigMaps:
+    nextcloud-mcp: nextcloud-mcp-dashboards
+```
+
+## Dashboard Variables
+
+The dashboard includes two variables:
+
+- **Data Source**: Select your Prometheus data source
+- **Namespace**: Filter metrics by Kubernetes namespace
+
+## Customization
+
+You can customize the dashboard by:
+
+1. Adjusting refresh rate (default: 30s)
+2. Modifying time range (default: last 6 hours)
+3. Adding new panels for specific metrics
+4. Adjusting thresholds in existing panels
+
+## Metrics Reference
+
+All metrics are documented in `/docs/observability.md`. Key metric prefixes:
+
+- `mcp_http_*` - HTTP server metrics
+- `mcp_tool_*` - MCP tool invocation metrics
+- `mcp_nextcloud_api_*` - Nextcloud API call metrics
+- `mcp_oauth_*` - OAuth token validation metrics
+- `mcp_vector_sync_*` - Vector database sync metrics
+- `mcp_db_*` - Database operation metrics