feat(observability): wire OpenTelemetry into MCP backend and marketing site

- Add OTEL_EXPORTER_OTLP_ENDPOINT env var to prod and stage MCP deployments pointing at Alloy in-cluster
- Add Neuron Platform Overview Grafana dashboard (request rate, latency percentiles, error rate, memory nodes, HTTP status distribution)
- Allow grafana/dashboards/*.json through .gitignore (was blocked by secrets rule)

servers/legion/k8s/neuron-technologies/prod/mcp-deployment.yaml

@@ -26,6 +26,9 @@ spec:
           ports:
             - name: http
               containerPort: 8080
+          env:
+            - name: OTEL_EXPORTER_OTLP_ENDPOINT
+              value: "http://alloy.monitoring.svc.cluster.local:4318"
           envFrom:
             - configMapRef:
                 name: neuron-prod-config

servers/legion/k8s/neuron-technologies/stage/mcp-deployment.yaml

@@ -24,6 +24,9 @@ spec:
           ports:
             - name: http
               containerPort: 8080
+          env:
+            - name: OTEL_EXPORTER_OTLP_ENDPOINT
+              value: "http://alloy.monitoring.svc.cluster.local:4318"
           envFrom:
             - configMapRef:
                 name: neuron-stage-config