add initial project files for Flutter app with platform-specific configs and basic routing setup

lib/pages/map/routing/osrm_routing_service.dart

@@ -0,0 +1,54 @@
+import 'dart:convert';
+
+import 'package:http/http.dart' as http;
+import 'package:latlong2/latlong.dart';
+
+class OsrmRoutingService {
+  const OsrmRoutingService({
+    this.baseUrl = 'https://router.project-osrm.org',
+    this.profile = 'driving',
+  });
+
+  final String baseUrl;
+  final String profile;
+
+  Future<List<LatLng>> fetchRoute(List<LatLng> waypoints) async {
+    if (waypoints.length < 2) {
+      return <LatLng>[];
+    }
+
+    final coordinates = waypoints
+        .map((point) => '${point.longitude},${point.latitude}')
+        .join(';');
+    final uri = Uri.parse(
+      '$baseUrl/route/v1/$profile/$coordinates'
+      '?overview=full&geometries=geojson',
+    );
+
+    final response = await http.get(uri);
+    if (response.statusCode != 200) {
+      throw Exception('Routing request failed (${response.statusCode})');
+    }
+
+    final payload = jsonDecode(response.body) as Map<String, dynamic>;
+    final routes = payload['routes'];
+    if (routes is! List || routes.isEmpty) {
+      throw Exception('No route returned');
+    }
+
+    final geometry = routes.first['geometry'] as Map<String, dynamic>?;
+    final coordinatesList = geometry?['coordinates'];
+    if (coordinatesList is! List || coordinatesList.isEmpty) {
+      throw Exception('Route geometry missing');
+    }
+
+    return coordinatesList.map((pair) {
+      if (pair is! List || pair.length < 2) {
+        throw Exception('Invalid coordinate pair in route geometry');
+      }
+      final lon = (pair[0] as num).toDouble();
+      final lat = (pair[1] as num).toDouble();
+      return LatLng(lat, lon);
+    }).toList();
+  }
+}