feat(claude): implement notification system with terminal bell for OSE perspective

## Context
In #765, we removed invalid notification-related settings from Claude Code settings files:
- `preferredNotifChannel`: "terminal_bell"
- `messageIdleNotifThresholdMs`: 60000

These settings were attempting to enable notifications but weren't recognized by Claude Code. This issue tracks properly implementing a notification system that supports the OSE (Outside and Slightly Elevated) perspective from our core principles.

## Problem Statement
The OSE perspective requires maintaining an external vantage point to see systems rather than getting entangled in details. Without proper notifications, it's easy to get absorbed into the work and lose this elevated perspective. A terminal bell or similar notification system would help maintain awareness of task completion, context switches, and system states.

## Desired Behavior
- Terminal bell notifications when Claude Code completes long-running tasks
- Configurable idle thresholds to remind about the OSE perspective
- Non-intrusive alerts that promote stepping back to review work
- Integration with the system's native notification capabilities

## Research Needed
1. Investigate Claude Code's official notification capabilities
2. Explore available notification channels (terminal bell, system notifications, etc.)
3. Determine correct configuration syntax and available options
4. Test different notification approaches for OSE effectiveness

## Acceptance Criteria
- [ ] Document available notification options in Claude Code
- [ ] Implement working notification configuration
- [ ] Test notifications support OSE perspective maintenance
- [ ] Update settings with valid, documented configuration
- [ ] Create procedure for notification setup if needed

## Keywords
Claude Code notifications, terminal bell, OSE perspective, preferredNotifChannel, messageIdleNotifThresholdMs, notification configuration, Outside and Slightly Elevated

## Related Issues
- Follows from #765 where invalid notification settings were removed

The issue names no repository files or tests; begin by investigating Claude Code’s official notification capabilities and valid configuration syntax, then compare terminal-bell and native notification channels. Done means documenting available options, testing a working configuration, updating settings with valid options, and creating a setup procedure if needed.

Written by the indexing model from the issue text.