feat: Add functionality to delete all discovered contacts

- Implemented a new method to remove all discovered contacts from the list.
- Added confirmation dialog for deleting all discovered contacts in the discovery screen.
- Updated localization files to include new strings for deleting all discovered contacts.
- Refactored contact import logic to streamline the process.
- Enhanced the discovery handling to notify users appropriately based on settings.

lib/l10n/app_localizations_de.dart

@@ -38,6 +38,9 @@ class AppLocalizationsDe extends AppLocalizations {
   @override
   String get common_delete => 'Löschen';
 
+  @override
+  String get common_deleteAll => 'Alles löschen';
+
   @override
   String get common_close => 'Schließen';
 
@@ -3200,4 +3203,12 @@ class AppLocalizationsDe extends AppLocalizations {
 
   @override
   String get discoveredContacts_deleteContact => 'Kontakt löschen';
+
+  @override
+  String get discoveredContacts_deleteContactAll =>
+      'Alle entdeckten Kontakte löschen';
+
+  @override
+  String get discoveredContacts_deleteContactAllContent =>
+      'Sind Sie sicher, dass Sie alle gefundenen Kontakte löschen möchten?';
 }