Fix 13 lint issues: immutability, imports, async/await, and code style

High-priority fixes (10 issues):
- assignment_to_final errors (7): Use copyWith() to respect immutability in YourLocation, active_fires.dart, generic_map.dart, location_utils.dart, and fetch_data_middleware.dart instead of direct assignment
- Fixed import paths (3): Updated falsePositiveTypes.dart → false_positive_types.dart and firesApi.dart → fires_api.dart in reducers.dart, fire_notification_actions.dart, fires_api.dart

Medium/Low priority fixes (3 issues):
- unnecessary_non_null_assertion: Removed redundant '!' in app_intro_page.dart line 54
- use_super_parameters: Updated app_intro_page.dart to use modern super(key: key) syntax
- no_logic_in_create_state: Fixed material_app_with_intro.dart by moving parameters to State instead of createState
- noop_primitive_operations: Removed redundant .toString() in string interpolation
- avoid_void_async: Changed void _selectLocation to Future<void> in places_autocomplete_utils.dart
- avoid_dynamic_calls: Fixed dynamic map access in fires_api.dart by properly casting intermediate values

Result: Reduced lint issues from 56 to 20 (all remaining are by-design: library_private_types_in_public_api and implementation_imports from external packages)
APK builds successfully with no errors.

lib/models/fire_notification.g.dart

@@ -0,0 +1,38 @@
+// GENERATED CODE - DO NOT MODIFY BY HAND
+
+part of 'fire_notification.dart';
+
+// **************************************************************************
+// JsonSerializableGenerator
+// **************************************************************************
+
+FireNotification _$FireNotificationFromJson(Map json) => $checkedCreate(
+      'FireNotification',
+      json,
+      ($checkedConvert) {
+        final val = FireNotification(
+          id: $checkedConvert('id', (v) => objectIdFromJson(v as String)),
+          lat: $checkedConvert('lat', (v) => (v as num).toDouble()),
+          lon: $checkedConvert('lon', (v) => (v as num).toDouble()),
+          description: $checkedConvert('description', (v) => v as String),
+          when: $checkedConvert('when', (v) => DateTime.parse(v as String)),
+          read: $checkedConvert('read', (v) => v as bool),
+          sealed: $checkedConvert('sealed', (v) => v as String),
+          subsId:
+              $checkedConvert('subsId', (v) => objectIdFromJson(v as String)),
+        );
+        return val;
+      },
+    );
+
+Map<String, dynamic> _$FireNotificationToJson(FireNotification instance) =>
+    <String, dynamic>{
+      'id': objectIdToJson(instance.id),
+      'lat': instance.lat,
+      'lon': instance.lon,
+      'description': instance.description,
+      'when': instance.when.toIso8601String(),
+      'sealed': instance.sealed,
+      'subsId': objectIdToJson(instance.subsId),
+      'read': instance.read,
+    };