Add error handling for stdout write failures to prevent uncaught EPIPE
exceptions when clients disconnect unexpectedly.

Changes:
- Add stdout error listener in start() to catch EPIPE and other errors
- Trigger graceful close when stdout errors occur
- Handle write errors in send() by rejecting the promise
- Clean up stdout error listener in close()

This prevents the Node.js process from crashing when a client disconnects
while the server is writing to stdout.

Fixes modelcontextprotocol#1564

…r cleanup

- Guard send() against closed transport (write on destroyed stream returns
  false and never drains/errors, hanging the promise)
- Fire onerror before onclose in stdout error handler
- Idempotent close() via _closed flag
- Symmetric error/drain listener cleanup in send() with settled guard
- Add changeset and tests covering error path, idempotent close, send
  rejection during backpressure, and send-after-close