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.lock

@@ -166,6 +166,11 @@ packages:
       url: "https://pub.dev"
     source: hosted
     version: "5.0.0"
+  flutter_localizations:
+    dependency: "direct main"
+    description: flutter
+    source: sdk
+    version: "0.0.0"
   flutter_map:
     dependency: "direct main"
     description:
@@ -340,10 +345,10 @@ packages:
     dependency: transitive
     description:
       name: intl
-      sha256: d6f56758b7d3014a48af9701c085700aac781a92a87a62b1333b46d8879661cf
+      sha256: "3df61194eb431efc39c4ceba583b95633a403f46c9fd341e550ce0bfa50e9aa5"
       url: "https://pub.dev"
     source: hosted
-    version: "0.19.0"
+    version: "0.20.2"
   latlong2:
     dependency: "direct main"
     description: