chore: disagg + router k8s recipe minor changes (#4050)

Signed-off-by: PeaBrane <yanrpei@gmail.com>

examples/backends/vllm/deploy/disagg.yaml

@@ -34,6 +34,7 @@ spec:
           args:
             - --model
             - Qwen/Qwen3-0.6B
+            - --is-decode-worker
     VllmPrefillWorker:
       dynamoNamespace: vllm-disagg
       envFromSecret: hf-token-secret

examples/backends/vllm/deploy/disagg_router.yaml

@@ -36,11 +36,12 @@ spec:
           args:
             - --model
             - Qwen/Qwen3-0.6B
+            - --is-decode-worker
     VllmPrefillWorker:
       dynamoNamespace: vllm-v1-disagg-router
       envFromSecret: hf-token-secret
       componentType: worker
-      replicas: 1
+      replicas: 2
       resources:
         limits:
           gpu: "1"