Use Mapbox tiles for web map

Dockerfile

@@ -1,9 +1,13 @@
 FROM ghcr.io/cirruslabs/flutter:stable AS build
 WORKDIR /app
+ARG MAPBOX_ACCESS_TOKEN=""
+ARG MAPBOX_STYLE="mapbox/streets-v12"
 COPY pubspec.* ./
 RUN flutter pub get
 COPY . .
-RUN flutter build web --release
+RUN flutter build web --release \
+  --dart-define=MAPBOX_ACCESS_TOKEN="$MAPBOX_ACCESS_TOKEN" \
+  --dart-define=MAPBOX_STYLE="$MAPBOX_STYLE"
 
 FROM nginx:1.27-alpine
 COPY nginx.conf /etc/nginx/conf.d/default.conf