Add payments-mcp (Layer 3 MCP surface), single-route pattern from the start

list-payments/get-payment (all 5 roles) and create-payment (admin
only — matches PaymentPermission's actual write-access logic, not
guessed). One KongRoute for GET/POST/DELETE, one ai-mcp-proxy
binding — avoids the duplicate-tool-name bug found and fixed on
customers-mcp (STATUS.md section 18), built correctly here instead
of repeating the two-route mistake.

Keycloak (local): mcp-payments-audience client scope + mcp-payments
resource client, attached to librechat as an optional scope, no
dedicated protocol mappers on the client itself.

kong/mcp/audit-log-body-capture.yaml

@@ -0,0 +1,27 @@
+# dev only: captures raw request/response bodies into kong.ctx.shared for
+# audit-log.yaml's custom_fields_by_lua to read back in the log phase.
+# Drop this file (and its bindings) to stop body capture without touching
+# audit-log.yaml itself — it degrades gracefully to metadata-only logging.
+apiVersion: configuration.konghq.com/v1
+kind: KongPlugin
+metadata:
+  name: ${NAME}-payments-mcp-audit-capture-request
+  namespace: ${NAMESPACE}
+plugin: pre-function
+config:
+  access:
+    - "kong.ctx.shared.audit_request_body = kong.request.get_raw_body()"
+---
+apiVersion: configuration.konghq.com/v1
+kind: KongPlugin
+metadata:
+  name: ${NAME}-payments-mcp-audit-capture-response
+  namespace: ${NAMESPACE}
+plugin: post-function
+config:
+  body_filter:
+    - |
+      local chunk = ngx.arg[1]
+      if chunk then
+        kong.ctx.shared.audit_response_body = (kong.ctx.shared.audit_response_body or "") .. chunk
+      end