feat(i18n): add capture prompt translations and locale init

- integrate flutter_localizations and delegates in MaterialApp
- use language-only supportedLocales; add resolution callback
- initialize I18n on app start and when switching language
- localize capture screen prompt via I18n.t
- schedule map centering via postFrame to avoid race conditions
- add flutter_localizations to pubspec

pubspec.yaml

@@ -30,6 +30,8 @@ environment:
 dependencies:
   flutter:
     sdk: flutter
+  flutter_localizations:
+    sdk: flutter
   cupertino_icons: ^1.0.8
   flutter_map: ^8.2.2
   flutter_map_marker_cluster: ^8.2.2