Fix: Replace tiles.wmflabs.org with tile.openstreetmap.org for reliable tile loading

tiles.wmflabs.org was causing DNS resolution failures on the device/emulator
(No address associated with hostname, errno = 7). Replaced with the official
OpenStreetMap tile server (tile.openstreetmap.org) which is more stable and reliable.

Removed subdomains configuration as it's not needed for the official OSM server.

- Updated FireMapLayer.osmcGrey in genericMap.dart
- Updated TileLayer in monitoredAreas.dart
- Fixes: Map tiles not loading due to network/DNS issues

lib/genericMap.dart

@@ -192,8 +192,7 @@ class _genericMapState extends State<genericMap> {
                   'https://{s}.tile.openstreetmap.fr/hot/{z}/{x}/{y}.png';
               break;
             case FireMapLayer.osmcGrey:
-              subdomains = ['a', 'b', 'c'];
-              baseLayer = 'https://tiles.wmflabs.org/bw-mapnik/{z}/{x}/{y}.png';
+              baseLayer = 'https://tile.openstreetmap.org/{z}/{x}/{y}.png';
               break;
             case FireMapLayer.esri:
               baseLayer =