feat(mcp): cap read volume per caller identity

A scope authorises a read and says nothing about volume. An agent reads a
thousand records in seconds where a person clicks ten, and until now nothing
noticed: the token is valid, the tool is permitted, the ACL passes. That gap
stopped being theoretical the day an autonomous run started reading the whole
catalog on a schedule.

identifier: credential keys the counter on the sub claim — the end user,
whoever is asking on their behalf — so an agent looping under one person's
identity spends that person's budget and cannot spend everyone's. Verified on
catalog: pm-user and ro-user hold separate counters.

Per-route namespace, so a busy domain cannot exhaust another's.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

kong/mcp/pluginbindings.yaml

@@ -51,3 +51,21 @@ spec:
       group: configuration.konghq.com
       kind: KongService
       name: ${NAME}-customers-mcp
+---
+apiVersion: configuration.konghq.com/v1alpha1
+kind: KongPluginBinding
+metadata:
+  name: ${NAME}-customers-mcp-rate-limiting-binding
+  namespace: ${NAMESPACE}
+spec:
+  controlPlaneRef:
+    type: konnectNamespacedRef
+    konnectNamespacedRef:
+      name: ${CONTROL_PLANE_REF_NAME}
+  pluginRef:
+    name: ${NAME}-customers-mcp-rate-limiting
+  targets:
+    routeRef:
+      group: configuration.konghq.com
+      kind: KongRoute
+      name: ${NAME}-customers-mcp