fix(frontend): error handling

mercury_frontend/lib/main.dart

@@ -37,7 +37,7 @@ class _SensorScreenState extends State<SensorScreen> {
   void initState() {
     super.initState();
     WidgetsBinding.instance.addPostFrameCallback((_) {
-      Provider.of<SensorProvider>(context, listen: false).fetchData();
+      Provider.of<SensorProvider>(context, listen: false).startAutoFetch(const Duration(seconds: 1));
     });
   }
 
@@ -49,8 +49,8 @@ class _SensorScreenState extends State<SensorScreen> {
         child: Consumer<SensorProvider>(
           builder: (context, sensorProvider, child) {
             if (sensorProvider.sensorData == null) {
-              if (sensorProvider.error != null) {
+              if (sensorProvider.exception != null) {
-                return Text('Error: ${sensorProvider.error}');
+                return Text('Error: ${sensorProvider.exception}');
               }
               return const CircularProgressIndicator();
             } else {

mercury_frontend/lib/sensor_provider.dart

@@ -1,3 +1,5 @@
+import 'dart:async';
+
 import 'package:flutter/material.dart';
 import 'sensor_data.dart';
 import 'sensor_service.dart';
@@ -6,18 +8,40 @@ class SensorProvider with ChangeNotifier {
   final SensorService _service = SensorService();
   SensorData? _sensorData;
 
-  Error? _error;
+  Exception? _exception;
 
   SensorData? get sensorData => _sensorData;
 
-  Error? get error => _error;
+  Exception? get exception => _exception;
+
+  Timer? _timer;
 
   Future<void> fetchData() async {
     try {
       _sensorData = await _service.fetchSensorData();
-    } catch (e) {
+    } on Exception catch (e) {
-      _error = e as Error;
+      _exception = e;
+      _sensorData = null;
     }
     notifyListeners();
   }
+  
+  void startAutoFetch(Duration interval) {
+    _timer = Timer.periodic(interval, (timer) async {
+      await fetchData();
+    });
+  }
+
+  // Stop auto-fetching
+  void stopAutoFetch() {
+    _timer?.cancel();
+    _timer = null;
+  }
+
+  // Dispose the timer when the provider is disposed
+  @override
+  void dispose() {
+    _timer?.cancel();
+    super.dispose();
+  }
 }