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/screens/contacts_screen.dart

@@ -222,7 +222,7 @@ class _ContactsScreenState extends State<ContactsScreen>
       final bytes = hex2Uint8List(hexString);
       final importContactFrame = buildImportContactFrame(bytes);
       _pendingOperations.add(ContactOperationType.import);
-      await connector.sendFrame(importContactFrame, expectsGenericAck: true);
+      connector.importContact(importContactFrame);
     } catch (e) {
       if (mounted) {
         ScaffoldMessenger.of(context).showSnackBar(

lib/screens/discovery_screen.dart

@@ -56,6 +56,25 @@ class _DiscoveryScreenState extends State<DiscoveryScreen> {
           subtitle: false,
         ),
         centerTitle: true,
+        actions: [
+          PopupMenuButton(
+            itemBuilder: (context) => [
+              PopupMenuItem(
+                child: Row(
+                  children: [
+                    const Icon(Icons.delete, color: Colors.red),
+                    const SizedBox(width: 8),
+                    Text(context.l10n.discoveredContacts_deleteContactAll),
+                  ],
+                ),
+                onTap: () {
+                  _deleteContacts(context, connector);
+                },
+              ),
+            ],
+            icon: const Icon(Icons.more_vert),
+          ),
+        ],
       ),
       body: Column(
         children: [
@@ -163,6 +182,30 @@ class _DiscoveryScreenState extends State<DiscoveryScreen> {
     }
   }
 
+  void _deleteContacts(BuildContext context, MeshCoreConnector connector) {
+    final l10n = context.l10n;
+    showDialog(
+      context: context,
+      builder: (context) => AlertDialog(
+        title: Text(l10n.common_deleteAll),
+        content: Text(l10n.discoveredContacts_deleteContactAllContent),
+        actions: [
+          TextButton(
+            onPressed: () => Navigator.pop(context),
+            child: Text(l10n.common_cancel),
+          ),
+          TextButton(
+            onPressed: () async {
+              Navigator.pop(context);
+              connector.removeAllDiscoveredContacts();
+            },
+            child: Text(l10n.common_deleteAll),
+          ),
+        ],
+      ),
+    );
+  }
+
   Widget _buildFilters(
     List<DiscoveryContact> filteredAndSorted,
     MeshCoreConnector connector,