Implements page edge hover detection and click handling:
- Hover near page edges (30px threshold) shows light outline
- Click on page edge opens PagePopup for template customization
- PagePopup component similar to ElementPopup but for @page rules
- Both popups coordinate to show only one at a time
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude <noreply@anthropic.com>
