Add tmux bell configuration for Claude Code notifications

## Summary
Add `set -g bell-action any` to the tmux configuration to enable terminal bell notifications from Claude Code.

## Context
Claude Code uses terminal bell notifications when tasks complete (after 60 seconds idle time). However, tmux by default doesn't propagate bell signals properly, causing users to miss completion notifications.

## Proposed Solution
Add the following to the tmux configuration:
```bash
set -g bell-action any
```

This will ensure bell notifications work properly in tmux sessions without requiring special terminal emulator configuration.

## Acceptance Criteria
- [ ] Add `set -g bell-action any` to tmux config
- [ ] Verify bell notifications work in tmux sessions
- [ ] No special iTerm2 or terminal-specific configuration required

Locate the tmux configuration and inspect where global tmux options are defined. Add the requested bell setting there, then verify bell notifications in a tmux session without terminal-specific configuration.

Written by the indexing model from the issue text.