Phase 3 completed: Flutter MVP with live streaming and auto-refresh

frontend/lib/providers/auth_provider.dart

@@ -0,0 +1,37 @@
+import 'package:flutter/material.dart';
+import 'package:shared_preferences/shared_preferences.dart';
+
+class AuthProvider with ChangeNotifier {
+  String? _token;
+  bool _isAuthenticated = false;
+
+  bool get isAuthenticated => _isAuthenticated;
+  String? get token => _token;
+
+  AuthProvider() {
+    _loadToken();
+  }
+
+  void _loadToken() async {
+    final prefs = await SharedPreferences.getInstance();
+    _token = prefs.getString('token');
+    _isAuthenticated = _token != null;
+    notifyListeners();
+  }
+
+  Future<void> login(String token) async {
+    _token = token;
+    _isAuthenticated = true;
+    final prefs = await SharedPreferences.getInstance();
+    await prefs.setString('token', token);
+    notifyListeners();
+  }
+
+  Future<void> logout() async {
+    _token = null;
+    _isAuthenticated = false;
+    final prefs = await SharedPreferences.getInstance();
+    await prefs.remove('token');
+    notifyListeners();
+  }
+}