Webclient. Areas favorites feature ...

- Added FavoritesStore (localStorage) for saving favorite areas
- New /areas/favorites screen with unstar button and empty state
- Star toggle button on areas tree screen
- Fixed sidebar hidden on areas-tree screen
- Set /areas/favorites as default areas page
- Fixed docs/device-spec.md duplicate section number
- Updated CLAUDE.md build instructions

Docs. Architecture, server API reference, dev guides. Tools moved to tools/