feat(api): add Kong RED metrics for LLM routes

Cluster-wide prometheus KongClusterPlugin (kong-metrics.yaml) +
chart-native ServiceMonitor (kong-values.yaml) expose
kong_http_requests_total/kong_latency_bucket/kong_bandwidth_bytes for
every route, LLM and otherwise. Dashboard filters to route=~"llm-.*"
for request rate, error rate, p95 upstream latency, and bandwidth.
Token-count metrics still need ai-proxy-advanced (Enterprise-only);
not attempted.

k8s/apps/api/kong-metrics.yaml

@@ -0,0 +1,19 @@
+# Cluster-wide Kong Prometheus plugin -- `global: "true"` label makes the
+# ingress controller apply it to every route on this Kong instance, so all
+# five LLM routes (ornith/reasoning/qwen/embeddings/rerank) get RED metrics
+# without touching llm-routes.yaml. Scraped via kong-values.yaml's
+# serviceMonitor (status listener, already on by chart default at :8100).
+apiVersion: configuration.konghq.com/v1
+kind: KongClusterPlugin
+metadata:
+  name: prometheus
+  annotations:
+    kubernetes.io/ingress.class: kong
+  labels:
+    global: "true"
+plugin: prometheus
+config:
+  status_code_metrics: true
+  latency_metrics: true
+  bandwidth_metrics: true
+  upstream_health_metrics: true