Scope the Map's side panel to the zoomed territory #89

When the Map is zoomed to one territory, the side panel still lists the hotspots of the whole repository, so files outside the zoomed territory appear (selecting one zooms out). A reader exploring one territory expects its own hotspots.

Done when

• While zoomed, the panel lists the hotspots of the zoomed territory and says so; zooming out restores the repository list.
• Selecting a file outside the territory still works as today.
• Tests cover the panel's scope.