* feat: add draggable sidebar resizer
- Add resizer handle between map and event panel
- Sidebar width adjustable from 300px to 50% screen width
- Default width remains 400px
- Auto-adjust on window resize
* fix: preserve map zoom when resizing sidebar
Only update viewport screen size without re-fitting the map
* fix: use window size for canvas to prevent map scaling on resize
- Canvas size now based on window instead of container
- Sidebar resize only clips the visible area, map stays same size
- Remove CSS stretch on canvas element
* docs: update sidebar-resizer spec with canvas fix
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