fix: Claude Code completion notifications not working

## Problem
Despite previous attempts to set up notifications when Claude Code completes work, notifications are not reliably working. This blocks autonomous operation as the user must constantly check if Claude is done.

## Current State
- Previous attempts to configure notifications have been made
- Notifications don't work consistently or at all
- User must actively monitor Claude's progress
- Prevents true hands-off operation

## Desired Behavior
- Get clear notification when Claude completes a task
- Notification should work across different platforms
- Should persist across Claude Code sessions
- Ideally support different notification channels

## Investigation Needed
1. What notification settings were previously tried?
2. Are there platform-specific issues?
3. Does the terminal bell setting work?
4. Are there alternative notification methods?

## Success Criteria
- User receives notification when Claude completes work
- Notifications work consistently across sessions
- User can configure notification preference
- Enables hands-off workflow

## Related Configuration
- Current settings show `notificationChannel: "terminal_bell"`
- May need platform-specific setup (see claude-code-settings.md)

Related: #592 (parent task)

Start by reviewing claude-code-settings.md and the current notificationChannel setting of terminal_bell, then compare the notification approaches previously tried. Determine the platform-specific setup and configuration needed so notifications persist across sessions, support a user preference, and reliably signal task completion.

Written by the indexing model from the issue text.