fix(settings): show excluding state on library index exclude action

Flush UI before the async unbind, disable repeat clicks, cancel an active
sync when needed, and label the button "Excluding…" / localized equivalent.

src/locales/nb/settings.ts

@@ -256,6 +256,7 @@ export const settings = {
   libraryIndexFullResync: 'Full resynkronisering',
   libraryIndexDeltaSync: 'Delta-synkronisering',
   libraryIndexExcludeServer: 'Ekskluder fra synkronisering',
+  libraryIndexExcludingServer: 'Ekskluderer…',
   libraryIndexExcludedTitle: 'Ekskludert fra synkronisering',
   libraryIndexIncludeServer: 'Inkluder igjen',
   libraryIndexStatus: 'Status',