phase3(critical-path): store + main + routes + nav components null-safe

- store/state + reducers: nullable AppState fields & reducer types
- main.dart: localeResolutionCallback Locale?, settings.name? guard
- routes.dart: fluro 2.0.5 HandlerFunc (BuildContext?) + params['x']!
- navigationbar/breadcrumbs/bottom_nav/text_link: nullable optional params/fields

lib/main.dart

@@ -103,7 +103,11 @@ class MyApp extends StatelessWidget {
         S.delegate,
       ],
       supportedLocales: S.delegate.supportedLocales,
-      localeResolutionCallback: (Locale locale, Iterable<Locale> supportedLocales) {
+      localeResolutionCallback: (Locale? locale, Iterable<Locale> supportedLocales) {
+        if (locale == null) {
+          store.dispatch(UpdateLocale(supportedLocales.first));
+          return supportedLocales.first;
+        }
         print('Language code: ${locale.languageCode}, Country code: ${locale.countryCode}');
         for (final supportedLocale in supportedLocales) {
           if (supportedLocale.languageCode == locale.languageCode) {
@@ -115,9 +119,9 @@ class MyApp extends StatelessWidget {
         return supportedLocales.first;
       },
       onGenerateRoute: (RouteSettings settings) {
-        final List<String> pathElements = settings.name.split('/');
+        final List<String> pathElements = settings.name?.split('/') ?? [];
         print('path elements: $pathElements');
-        if (pathElements[0] != '') {
+        if (pathElements.isEmpty || pathElements[0] != '') {
           return null;
         }
         if (pathElements[1] == 'me') {