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/ro/settings.ts

@@ -263,6 +263,7 @@ export const settings = {
   libraryIndexFullResync: 'Resincronizare completă',
   libraryIndexDeltaSync: 'Sincronizare delta',
   libraryIndexExcludeServer: 'Exclude din sincronizare',
+  libraryIndexExcludingServer: 'Se exclude…',
   libraryIndexExcludedTitle: 'Excluse din sincronizare',
   libraryIndexIncludeServer: 'Include din nou',
   libraryIndexStatus: 'Stare',