feat(ui): add animated screen transitions and guest onboarding

Improve app UX by adding animated transitions for screen switches
and introducing a persisted guest onboarding flow.

- Add AnimatedSwitcher-based fade+slide transitions for screens and
  tab switches for smoother navigation.
- Persist a 'user_mode' SharedPreferences key and provide guest
  helpers to mark users as guest and influence routing.
- Update SignInScreen continue-as-guest action to set onboarding and
  guest flags and navigate to MainScreen.
- Normalize locales in LocaleProvider to language-only values and
  persist normalized language codes to ensure compatibility with
  Flutter localization delegates.
- Replace Row with Wrap in ReportCard to improve spacing and
  responsiveness.

No breaking changes

lib/l10n/locale_provider.dart

@@ -19,19 +19,25 @@ class LocaleProvider extends ChangeNotifier {
   /// Initialize the locale provider
   Future<void> init() async {
     _prefs = await SharedPreferences.getInstance();
-    final savedLanguage = _prefs.getString(_languageKey) ?? _defaultLanguage;
-    _locale = Locale(savedLanguage);
+    final saved = _prefs.getString(_languageKey) ?? _defaultLanguage;
+    final parts = saved.split(RegExp(r'[-_]'));
+    // Normalize and keep language-only locales so they match Global*Localizations delegates
+    final language = parts.isNotEmpty && parts[0].isNotEmpty ? parts[0] : _defaultLanguage;
+    _locale = Locale(language);
     await I18n.init(_locale);
     notifyListeners();
   }
 
   /// Set the locale and persist the change
   Future<void> setLocale(Locale locale) async {
-    if (_locale == locale) return;
+    // Normalize to language-only locale to ensure compatibility with delegates
+    final normalized = Locale(locale.languageCode);
+    if (_locale == normalized) return;
 
-    _locale = locale;
-    await _prefs.setString(_languageKey, locale.languageCode);
-    await I18n.init(locale);
+    _locale = normalized;
+    final saveValue = _locale.languageCode;
+    await _prefs.setString(_languageKey, saveValue);
+    await I18n.init(_locale);
     notifyListeners();
   }
 
@@ -45,7 +51,7 @@ class LocaleProvider extends ChangeNotifier {
   Future<void> setEnglish() async {
     await setLocale(const Locale('en'));
   }
-
+  
   /// Set language to Bahasa Malaysia
   Future<void> setMalay() async {
     await setLocale(const Locale('ms'));