Sound notifications for turn completion and user input required

What feature would you like to see?

When running long-running prompts, users may switch to other tasks and miss when the prompt completes or requires input. Currently, there is no audible alert.

Proposed Solution

Add optional sound notifications that play:

1. When a turn completes
2. When user input is required

Configuration

Extend the existing [tui] config section to support sound:

[tui]
# Existing notification options
notifications = true

# New sound options (proposed)
sound_on_complete = true        # Play sound when turn completes
sound_on_input_required = true  # Play sound when input is needed

For custom sounds, users could specify a command:

[tui]
sound_on_complete = ["afplay", "/System/Library/Sounds/Glass.aiff"]
sound_on_input_required = ["afplay", "/System/Library/Sounds/Ping.aiff"]

Implementation Approach

• Use terminal bell (\x07) as the default cross-platform sound
• Support custom sound commands (similar to the existing notifications = ["command"] pattern)
• Follow the existing notification backend pattern in tui/src/notifications/

Why This Matters

• Improves productivity by alerting users to completed tasks
• Prevents missed approval requests that could block progress
• Follows existing patterns in the codebase (mirrors the Notifications enum design)

Additional information

_No response_