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/templates/deployment.yaml

@@ -56,6 +56,11 @@ spec:
             - name: http
               containerPort: {{ include "nextcloud-mcp-server.port" . }}
               protocol: TCP
+            {{- if .Values.observability.metrics.enabled }}
+            - name: metrics
+              containerPort: {{ .Values.observability.metrics.port }}
+              protocol: TCP
+            {{- end }}
           env:
             # Nextcloud connection
             - name: NEXTCLOUD_HOST
@@ -200,6 +205,27 @@ spec:
               value: {{ .Values.openai.baseUrl | quote }}
             {{- end }}
             {{- end }}
+            # Observability
+            - name: METRICS_ENABLED
+              value: {{ .Values.observability.metrics.enabled | quote }}
+            - name: METRICS_PORT
+              value: {{ .Values.observability.metrics.port | quote }}
+            {{- if .Values.observability.tracing.enabled }}
+            - name: OTEL_ENABLED
+              value: "true"
+            - name: OTEL_EXPORTER_OTLP_ENDPOINT
+              value: {{ .Values.observability.tracing.endpoint | quote }}
+            - name: OTEL_SERVICE_NAME
+              value: {{ .Values.observability.tracing.serviceName | quote }}
+            - name: OTEL_TRACES_SAMPLER_ARG
+              value: {{ .Values.observability.tracing.samplingRate | quote }}
+            {{- end }}
+            - name: LOG_FORMAT
+              value: {{ .Values.observability.logging.format | quote }}
+            - name: LOG_LEVEL
+              value: {{ .Values.observability.logging.level | quote }}
+            - name: LOG_INCLUDE_TRACE_CONTEXT
+              value: {{ .Values.observability.logging.includeTraceContext | quote }}
             {{- with .Values.extraEnv }}
             {{- toYaml . | nindent 12 }}
             {{- end }}