Make Codex app notification sounds louder or configurable

What variant of Codex are you using?

Codex app version 26.506.31421 (2620) on macOS.

What feature would you like to see?

The Codex app already supports desktop notifications, but the current notification sound is too quiet and easy to miss when the app is running in the background.

I would like Codex app notifications to be more noticeable, especially for:

• Turn completion
• Input required
• Permission required

Possible solutions:

• Provide a louder built-in notification sound
• Let users choose from several notification sounds
• Add a volume or intensity setting for Codex app notifications
• Allow a custom local sound file
• Optionally repeat the alert for input-required or permission-required states until the user returns

Additional information

I understand from #3962 that the Codex app uses standard OS desktop notifications. Even so, the current alert is easy to miss in real use, so having an app-level way to make notifications louder or more noticeable would improve long-running agent workflows.