feat: add MainScreen with tracking toggle and status display

lib/main_screen.dart

@@ -0,0 +1,158 @@
+import 'package:flutter/material.dart';
+import 'package:traccar_client/bridge/location_bridge.dart';
+import 'package:traccar_client/preferences.dart';
+import 'package:traccar_client/settings_screen.dart';
+import 'package:traccar_client/status_screen.dart';
+
+class MainScreen extends StatefulWidget {
+  const MainScreen({super.key});
+
+  @override
+  State<MainScreen> createState() => _MainScreenState();
+}
+
+class _MainScreenState extends State<MainScreen> {
+  bool _isTracking = false;
+  String _lastLat = '--';
+  String _lastLon = '--';
+  String _lastSpeed = '--';
+  String _lastTime = '--';
+
+  @override
+  void initState() {
+    super.initState();
+    _initLocationStream();
+  }
+
+  void _initLocationStream() {
+    LocationBridge.locationUpdates.listen((location) {
+      if (mounted) {
+        setState(() {
+          _lastLat = location['latitude']?.toStringAsFixed(4) ?? '--';
+          _lastLon = location['longitude']?.toStringAsFixed(4) ?? '--';
+          _lastSpeed = location['speed'] != null
+              ? '${(location['speed'] * 3.6).toStringAsFixed(0)} km/h'
+              : '--';
+          _lastTime = location['timestamp'] != null
+              ? _formatTime(DateTime.fromMillisecondsSinceEpoch(location['timestamp']))
+              : '--';
+        });
+      }
+    });
+  }
+
+  String _formatTime(DateTime dt) {
+    return '${dt.hour.toString().padLeft(2, '0')}:${dt.minute.toString().padLeft(2, '0')}:${dt.second.toString().padLeft(2, '0')}';
+  }
+
+  Future<void> _toggleTracking() async {
+    if (_isTracking) {
+      await LocationBridge.stopTracking();
+    } else {
+      await LocationBridge.startTracking();
+    }
+    setState(() {
+      _isTracking = !_isTracking;
+    });
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    return Scaffold(
+      appBar: AppBar(
+        title: const Text('Traccar Client'),
+        centerTitle: true,
+      ),
+      body: Padding(
+        padding: const EdgeInsets.all(16.0),
+        child: Column(
+          crossAxisAlignment: CrossAxisAlignment.stretch,
+          children: [
+            _buildStatusCard(),
+            const SizedBox(height: 24),
+            _buildTrackingToggle(),
+            const Spacer(),
+            _buildActionButtons(),
+          ],
+        ),
+      ),
+    );
+  }
+
+  Widget _buildStatusCard() {
+    return Card(
+      child: Padding(
+        padding: const EdgeInsets.all(16.0),
+        child: Column(
+          crossAxisAlignment: CrossAxisAlignment.start,
+          children: [
+            Text(
+              'Last Location',
+              style: Theme.of(context).textTheme.titleMedium,
+            ),
+            const SizedBox(height: 16),
+            _buildInfoRow('Lat', _lastLat),
+            _buildInfoRow('Lon', _lastLon),
+            _buildInfoRow('Speed', _lastSpeed),
+            _buildInfoRow('Time', _lastTime),
+          ],
+        ),
+      ),
+    );
+  }
+
+  Widget _buildInfoRow(String label, String value) {
+    return Padding(
+      padding: const EdgeInsets.symmetric(vertical: 4.0),
+      child: Row(
+        mainAxisAlignment: MainAxisAlignment.spaceBetween,
+        children: [
+          Text(label),
+          Text(value, style: const TextStyle(fontWeight: FontWeight.bold)),
+        ],
+      ),
+    );
+  }
+
+  Widget _buildTrackingToggle() {
+    return SwitchListTile(
+      title: Text(_isTracking ? 'Tracking: ON' : 'Tracking: OFF'),
+      subtitle: Text(_isTracking ? 'Location updates active' : 'Tap to start tracking'),
+      value: _isTracking,
+      onChanged: (_) => _toggleTracking(),
+      activeColor: Colors.green,
+    );
+  }
+
+  Widget _buildActionButtons() {
+    return Row(
+      children: [
+        Expanded(
+          child: ElevatedButton.icon(
+            onPressed: () {
+              Navigator.push(
+                context,
+                MaterialPageRoute(builder: (_) => const SettingsScreen()),
+              );
+            },
+            icon: const Icon(Icons.settings),
+            label: const Text('Settings'),
+          ),
+        ),
+        const SizedBox(width: 16),
+        Expanded(
+          child: ElevatedButton.icon(
+            onPressed: () {
+              Navigator.push(
+                context,
+                MaterialPageRoute(builder: (_) => const StatusScreen()),
+              );
+            },
+            icon: const Icon(Icons.logs),
+            label: const Text('Status/Logs'),
+          ),
+        ),
+      ],
+    );
+  }
+}