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/services/share_service.dart

@@ -18,35 +18,18 @@ class ShareService {
     );
     
     if (response.statusCode == 201) {
-      final data = jsonDecode(response.body);
-      return {
-        'geo_id': data['geo_id'],
-        'share_id': data['share_id'],
-      };
+      try {
+        final data = jsonDecode(response.body) as Map<String, dynamic>;
+        return {
+          'geo_id': data['geo_id']?.toString() ?? '',
+          'share_id': data['share_id']?.toString() ?? '',
+        };
+      } catch (e) {
+        throw Exception('Failed to parse response: $e | Body: ${response.body.substring(0, response.body.length > 200 ? 200 : response.body.length)}');
+      }
     } else {
-      throw Exception('Failed to create share link');
-    }
-  }
-
-  Future<Map<String, dynamic>> getPosition(String token, String uniqueId) async {
-    final response = await _client.get(
-      Uri.parse('${ApiConfig.watchUrl}?unique_id=$uniqueId'),
-      headers: {
-        'Authorization': 'Bearer $token',
-      },
-    );
-    
-    if (response.statusCode == 200) {
-      final data = jsonDecode(response.body);
-      return {
-        'id': data['id'],
-        'x': data['x'],
-        'y': data['y'],
-        'created_at': data['created_at'],
-        'expires_at': data['expires_at'],
-      };
-    } else {
-      throw Exception('Share link not found or no position available');
+      final errorBody = response.body.length > 200 ? response.body.substring(0, 200) : response.body;
+      throw Exception('Failed to create share link: ${response.statusCode} - $errorBody');
     }
   }
 
@@ -59,15 +42,15 @@ class ShareService {
     );
     
     if (response.statusCode == 200) {
-      final data = jsonDecode(response.body);
+      final data = jsonDecode(response.body) as Map<String, dynamic>;
       return {
         'x': data['x'],
         'y': data['y'],
-        'created_at': data['created_at'],
-        'expires_at': data['expires_at'],
+        'last_update': data['last_update']?.toString() ?? '',
+        'expires_at': data['expires_at']?.toString() ?? '',
       };
     } else {
       throw Exception('Share link not found or no position available');
     }
   }
-}
+}