refactor(files): Adjust `useNavigation` composable to enforce active view

refactor(files): Adjust `useNavigation` composable to enforce active view

In some cases it is guaranteed that we have a proper active view,
e.g. when the file list is loaded (so within FileEntry* components).
This does not change anything but the Typescript types,
so the `currentView` is typed as `View` instead of `View | null´.

Signed-off-by: Ferdinand Thiessen <opensource@fthiessen.de>