Implement system theme support and dark mode infrastructure

Add comprehensive theme management system with iOS system integration:

- System theme detection: App follows iOS dark/light mode preferences via ThemeMode.system
- Theme provider: Centralized theme state management with Riverpod (defaults to dark mode)
- Settings toggle: Segmented button UI for Light/Dark/Auto theme selection
- iOS system UI: Status bar and navigation bar adapt to current theme brightness

Dark mode map styling (Android-ready):
- DarkModeMapComponent: Reactive theme change detection with didChangeDependencies
- Map style application: Custom dark JSON style for navigation maps
- Theme-aware styling: Automatically applies/resets map style on theme changes
- Note: Map styling currently Android-only due to iOS SDK limitations

Updates:
- main.dart: System UI overlay styling for iOS, theme provider integration
- settings_page.dart: SegmentedButton theme toggle with icons
- providers.dart: themeModeProvider for app-wide theme state
- dark_mode_map.dart: Theme reactivity and style application logic
- navigation_page.dart: Theme detection infrastructure (prepared for future use)

Design philosophy:
- Follow system preferences by default for native iOS experience
- Manual override available for user preference
- Clean separation between Flutter UI theming and native map styling

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

lib/components/dark_mode_map.dart

@@ -31,6 +31,7 @@ class _DarkModeMapComponentState extends State<DarkModeMapComponent> {
   bool _isInitializing = false;
   bool _isStartingNavigation = false;
   String _loadingMessage = 'Initializing...';
+  Brightness? _lastBrightness;
 
   @override
   void initState() {
@@ -38,6 +39,20 @@ class _DarkModeMapComponentState extends State<DarkModeMapComponent> {
     _initializeNavigation();
   }
 
+  @override
+  void didChangeDependencies() {
+    super.didChangeDependencies();
+
+    // Detect theme changes and reapply map style
+    final currentBrightness = Theme.of(context).brightness;
+    if (_lastBrightness != null &&
+        _lastBrightness != currentBrightness &&
+        _navigationController != null) {
+      _applyDarkModeStyle();
+    }
+    _lastBrightness = currentBrightness;
+  }
+
   Future<void> _initializeNavigation() async {
     if (_isInitializing || _isSessionInitialized) return;
 
@@ -121,14 +136,35 @@ class _DarkModeMapComponentState extends State<DarkModeMapComponent> {
     if (!mounted || _navigationController == null) return;
 
     try {
-      // Apply dark mode style configuration for Google Maps
-      // This reduces eye strain in low-light environments
       if (!mounted) return;
 
       final isDarkMode = Theme.of(context).brightness == Brightness.dark;
       if (isDarkMode) {
-        // Dark map style with warm accent colors
-        await _navigationController!.setMapStyle(_getDarkMapStyle());
+        // Dark mode style - Note: Currently only supported on Android
+        const simpleDarkStyle = '''[
+          {
+            "elementType": "geometry",
+            "stylers": [{"color": "#242424"}]
+          },
+          {
+            "elementType": "labels.text.fill",
+            "stylers": [{"color": "#746855"}]
+          },
+          {
+            "elementType": "labels.text.stroke",
+            "stylers": [{"color": "#242424"}]
+          },
+          {
+            "featureType": "water",
+            "elementType": "geometry",
+            "stylers": [{"color": "#17263c"}]
+          }
+        ]''';
+
+        await _navigationController!.setMapStyle(simpleDarkStyle);
+      } else {
+        // Reset to default light style
+        await _navigationController!.setMapStyle(null);
       }
     } catch (e) {
       if (mounted) {