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.yaml

@@ -0,0 +1,17 @@
+apiVersion: configuration.konghq.com/v1
+kind: KongPlugin
+metadata:
+  name: ${NAME}-payments-mcp-audit-log
+  namespace: ${NAMESPACE}
+plugin: http-log
+# dev only: the raw Authorization (JWT) header is captured in clear text,
+# not acceptable as-is for a non-dev environment. request_body/response_body
+# below read from kong.ctx.shared, populated by audit-log-body-capture.yaml
+# — nil (and silently omitted) if that file isn't applied.
+config:
+  http_endpoint: ${AUDIT_LOG_ENDPOINT}
+  method: POST
+  content_type: application/json
+  custom_fields_by_lua:
+    request_body: "return kong.ctx.shared.audit_request_body"
+    response_body: "return kong.ctx.shared.audit_response_body"