Refactor contacts management and improve path handling

- Updated ContactsProvider to initialize with device public key for filtering out self contacts.
- Added methods to check if a contact has a learned routing path and to get path quality indicators.
- Enhanced AppProvider to initialize ContactsProvider with device public key.
- Modified ConnectionProvider to log path status when sending messages.
- Created ContactStorageService for persisting contacts to local storage.
- Removed import/export functionality from MapManagementScreen.
- Updated UI components in DirectMessageSheet and SarUpdateSheet to use theme colors.
- Removed file_picker dependency from pubspec.yaml and generated plugin registrant.

lib/main.dart

@@ -68,7 +68,13 @@ class _MeshCoreSarAppState extends State<MeshCoreSarApp> {
       providers: [
         // Core providers
         ChangeNotifierProvider(create: (_) => ConnectionProvider()),
-        ChangeNotifierProvider(create: (_) => ContactsProvider()),
+        ChangeNotifierProvider(
+          create: (_) {
+            // Don't initialize here - it will be initialized in AppProvider.initialize()
+            // after connection is established and device info is available
+            return ContactsProvider();
+          },
+        ),
         ChangeNotifierProvider(
           create: (_) {
             final provider = MessagesProvider();