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

assets/lang/en.json

@@ -7,6 +7,7 @@
   "btn.capture": "Capture",
   "btn.gallery": "Gallery",
   "btn.camera": "Camera",
+  "capture.prompt": "Take a photo of the issue",
   "btn.next": "Next",
   "btn.submit": "Submit",
   "btn.save": "Save",

assets/lang/ms.json

@@ -7,6 +7,7 @@
   "btn.capture": "Tangkap",
   "btn.gallery": "Galeri",
   "btn.camera": "Kamera",
+  "capture.prompt": "Ambil gambar isu",
   "btn.next": "Seterusnya",
   "btn.submit": "Hantar",
   "btn.save": "Simpan",