Add fingerprint (local_auth) session + 3-min inactivity timeout (default), activity resets timer, settings: biometric toggle + timeout picker

lib/auth_screen.dart

@@ -5,7 +5,8 @@ import 'package:login_vault_app/auth_service.dart';
 import 'package:login_vault_app/dashboard_screen.dart';
 import 'package:login_vault_app/theme_provider.dart';
 
-/// First-launch screen: register with email+password, or with Google.
+/// First screen: register, or (if registered) re-authenticate.
+/// If a valid session exists, skip straight to the Dashboard.
 class AuthScreen extends StatefulWidget {
   final AuthService auth;
   const AuthScreen({super.key, required this.auth});
@@ -17,12 +18,29 @@ class AuthScreen extends StatefulWidget {
 class _AuthScreenState extends State<AuthScreen> {
   final _emailCtrl = TextEditingController();
   final _passCtrl = TextEditingController();
-  bool _isLogin = true; // toggle register/login
+  bool _isLogin = true;
   bool _busy = false;
   String? _error;
 
+  @override
+  void initState() {
+    super.initState();
+    _trySilentAuth();
+  }
+
+  /// On open: if a valid session is present, go straight to Dashboard.
+  Future<void> _trySilentAuth() async {
+    final timeout = await widget.auth.getTimeoutMinutes();
+    final valid = await widget.auth.hasValidSession(timeout);
+    if (valid && mounted) {
+      final email = await widget.auth.getEmail() ?? '';
+      _goToDashboard(email);
+    }
+  }
+
   void _goToDashboard(String email) {
     if (!mounted) return;
+    widget.auth.openSession(); // refresh session timestamp
     Navigator.of(context).pushReplacement(
       MaterialPageRoute(
         builder: (_) => DashboardScreen(