Add Android support with configurable server URL and location permissions

- Add shared_preferences for persisting server URL
- Add SettingsService and PlatformService
- Add server URL input field on non-web platforms
- Make ApiConfig baseUrl configurable at runtime
- Add Android location permissions (ACCESS_FINE/COURSE_LOCATION, INTERNET)
- Request location permission on login and map init
- Fix geo_id type: use String instead of int (UUID format)
- Align share_service with API spec: remove unique_id, use share_id only
- Fix watch endpoint response: last_update instead of created_at
- Add error handling with SnackBars for geo operations
- Wrap login screen in SingleChildScrollView for keyboard handling
- Update map tile layer with userAgentPackageName for OSM

lib/providers/share_provider.dart

@@ -5,7 +5,7 @@ class ShareProvider with ChangeNotifier {
   final ShareService _shareService;
   
   String _shareId = '';
-  int _geoId = 0;
+  String _geoId = '';
   bool _isLoading = false;
   String _error = '';
   
@@ -19,7 +19,7 @@ class ShareProvider with ChangeNotifier {
       : _shareService = shareService ?? ShareService();
   
   String get shareId => _shareId;
-  int get geoId => _geoId;
+  String get geoId => _geoId;
   bool get isLoading => _isLoading;
   String get error => _error;
   Map<String, dynamic>? get position => _position;
@@ -34,8 +34,8 @@ class ShareProvider with ChangeNotifier {
     
     try {
       final result = await _shareService.createShare(token, x, y);
-      _geoId = result['geo_id'];
-      _shareId = result['share_id'];
+      _geoId = result['geo_id']?.toString() ?? '';
+      _shareId = result['share_id']?.toString() ?? '';
       notifyListeners();
     } catch (e) {
       _error = e.toString();
@@ -47,13 +47,13 @@ class ShareProvider with ChangeNotifier {
     }
   }
   
-  Future<void> getPosition(String token, String shareID) async {
+  Future<void> getPosition(String token, String shareId) async {
     _isLoading = true;
     _error = '';
     notifyListeners();
     
     try {
-      _position = await _shareService.getPosition(token, shareID);
+      _position = await _shareService.getPositionByShareId(token, shareId);
       notifyListeners();
     } catch (e) {
       _error = e.toString();
@@ -67,7 +67,7 @@ class ShareProvider with ChangeNotifier {
   
   void clearShare() {
     _shareId = '';
-    _geoId = 0;
+    _geoId = '';
     _position = null;
     notifyListeners();
   }