feat: play sound when agent is finished if notificationSound setting …

[sutt]

Per #2372 create setting which allows sound to play when agent is finished.

• This is off by default.
• If enabled via "notificationSound": true, will use system bell.
• If notificationSound is not a boolean, a system-specific command/sound can be specified for this action, see below:

Full possible config:

 {
    // System bell (most portable, but often disabled in terminals)
    "notificationSound": true,

    // Or custom command:
    // macOS
    "notificationSound": "afplay /System/Library/Sounds/Glass.aiff",

    // Linux (with PulseAudio)
    "notificationSound": "paplay
  /usr/share/sounds/freedesktop/stereo/complete.oga",

    // Windows
    "notificationSound": "powershell -c (New-Object Media.SoundPlayer
  'C:\\Windows\\Media\\chimes.wav').PlaySync()"
  }

Audio / Visual Demo

https://github.com/user-attachments/assets/a9913165-4414-413b-bbbe-c4c11677c5ff