Session name is sometimes missing from notifications (notify plugin)

Summary

The bundled notify plugin (kdcokenny/opencode-notify) sometimes does not
include the session name in the desktop notification, so you can't tell which
session it belongs to.

Verified in the plugin source (~/.config/opencode/plugins/notify.ts)

• sessionTitle (from session.data.title, default "Task") is used only in
  the session.idle handler ("Ready for review"). For session.error
  ("Something went wrong"), permission.asked/updated ("Waiting for you") and
  question.asked ("Question for you") the session name is not included at
  all — message is a hardcoded string.
• On the Linux desktop fallback, node-notifier maps subtitle (which carries
  sessionTitle in the idle handler) to category, which notify-send does
  not render — so the session name is also lost there.

Expected

Include the session name in every notification (error, permission, question,
and ready/idle).