P3.8: Restrict llm-serving ingress to api-gateway only (#15)

## Summary

Replaces hand-applied `llm-serving-default-deny` NetworkPolicy with a git-managed, namespace-scoped policy that only allows traffic from the api-gateway.

**Issue:** #13

Co-authored-by: rock <[email protected]>

k8s/apps/llm-serving/kustomization.yaml

@@ -14,5 +14,6 @@ resources:
   - ornith.yaml
   - reasoning.yaml
   - reranker.yaml
+  - networkpolicy.yaml
 # No namespace transformer: every file sets its own, and the transformer would
 # rewrite metadata.namespace on anything cross-namespace added later.

k8s/apps/llm-serving/networkpolicy.yaml

@@ -0,0 +1,62 @@
+# NetworkPolicy for LLM inference engines (llm-serving namespace).
+#
+# These pods have NO auth — vLLM, Ollama, and TEI accept any request.
+# All access MUST go through the api-gateway, which validates JWTs and
+# injects identity headers (X-Forwarded-User, X-Auth-Verified).
+#
+# Replaces the hand-applied llm-serving-default-deny policy that used
+# `llm-client: "true"` pod label as a selector — any pod in any namespace
+# could self-grant access by adding that label, which defeats the purpose.
+#
+# This policy restricts ingress to:
+#   1. api namespace (gateway) — the sole entry point for inference
+#   2. monitoring namespace — Prometheus scraping vLLM/TEI /metrics
+#   3. intra-namespace — pod-to-pod (future: multi-replica comms)
+apiVersion: networking.k8s.io/v1
+kind: NetworkPolicy
+metadata:
+  name: llm-serving-ingress
+  namespace: llm-serving
+  labels:
+    app.kubernetes.io/part-of: llm-serving
+spec:
+  podSelector:
+    matchLabels:
+      app.kubernetes.io/part-of: llm-serving
+  policyTypes:
+    - Ingress
+  ingress:
+    # Allow from api-gateway (namespace: api)
+    # Gateway proxies /v1/chat/completions, /v1/embeddings, /v1/rerank
+    - from:
+        - namespaceSelector:
+            matchLabels:
+              kubernetes.io/metadata.name: api
+      ports:
+        - protocol: TCP
+          port: 8080   # vLLM, Ollama HTTP
+        - protocol: TCP
+          port: 80      # KServe predictor services
+        - protocol: TCP
+          port: 8000    # vLLM direct (some configs)
+        - protocol: TCP
+          port: 11434   # Ollama native port
+    # Allow Prometheus scraping from monitoring namespace
+    # vLLM: :8080/metrics, TEI: :9000/metrics
+    - from:
+        - namespaceSelector:
+            matchLabels:
+              kubernetes.io/metadata.name: monitoring
+      ports:
+        - protocol: TCP
+          port: 8080
+        - protocol: TCP
+          port: 9000
+    # Allow intra-namespace (pod-to-pod within llm-serving)
+    - from:
+        - podSelector:
+            matchLabels:
+              app.kubernetes.io/part-of: llm-serving
+      ports:
+        - protocol: TCP
+          port: 8080