- Add theme store with light/dark/system modes and ThemeToggle component
- Prevent flash of wrong theme on initial load via inline script
- Add ExportPreviewModal for previewing session exports before download
- Add copy-to-clipboard functionality to session export
- Implement keyboard shortcuts for tree navigation (1-9 options, Esc back, Enter continue)
- Display keyboard hints in tree navigation UI
- Fix findNode to safely handle undefined structure parameter
- Update page title to "Apoklisis"
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
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