fix(ext/web,runtime): match MessagePort by host-object brand
The MessagePort rewrite installed a "MessagePort" transferable
receive callback in node:worker_threads that returns Node-style
instances (different prototype, same hostObjectBrand). Three
sites still filtered `MessageEvent.ports` by the Web MessagePort
prototype and so dropped Node-style ports on the floor:
- runtime/js/99_main.js dispatchWorkerMessage
- runtime/js/11_workers.js Worker#dispatchMessage
- ext/web/13_message_port.js dispatchPortMessageData
That broke tests/unit/worker_test.ts "Send MessagePorts from / to
workers" -- `ev.ports[0]` was undefined.
Switch all three to a brand check so either prototype carries
through MessageEvent.ports as expected.
