fix: wire grant verifier

deploy/20-deployment.yaml

@@ -33,6 +33,10 @@ spec:
             - containerPort: 8000
               name: http1
               protocol: TCP
+          env:
+            - name: A2A_GRANT_VERIFYING_KEY
+              valueFrom:
+                secretKeyRef: {name: platform-secrets, key: grant_verifying_key}
           readinessProbe:
             httpGet: {path: /healthz, port: 8000}
             initialDelaySeconds: 2