fix: hide action button after uninstalling or restoring apps

[coderang-gk]

Fixes #160 floating action button remained visible after uninstalling or restoring apps, even when no apps were selected. This fix ensures the button properly disappears when the selection is empty.

[samolego]

Where do you actually use isSelectionMode? Also, can't we just edit the CantaApp#MainContent and, as you've already done, the AppListViewModel?

[samolego]

Here you're still using the old value like before: https://github.com/coderang-gk/Canta/blob/2309d52b09a14d4a3133fcb01e974a22a3752955/app/src/main/java/org/samo_lego/canta/ui/CantaApp.kt#L126

[samolego]

I assume you have tested & built the apk too?

[coderang-gk]

I assume you have tested & built the apk too?

yes, works fine

[samolego]

Thanks for your contribution!