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/widgets/general/breadcrumbs.dart

@@ -7,10 +7,10 @@ import '../../routes.dart';
 import 'navigationbar.dart';
 
 class BreadCrumbs extends StatelessWidget {
-  final List<BreadCrumb> breadCrumbs;
+  final List<BreadCrumb>? breadCrumbs;
   final bool hasBack;
-  final OnBackPress onBackPress;
-  const BreadCrumbs(this.hasBack, {this.breadCrumbs, Key key, this.onBackPress}) : super(key: key);
+  final OnBackPress? onBackPress;
+  const BreadCrumbs(this.hasBack, {this.breadCrumbs, Key? key, this.onBackPress}) : super(key: key);
 
   @override
   Widget build(BuildContext context) {
@@ -49,11 +49,11 @@ class BreadCrumbs extends StatelessWidget {
       ));
     }
     if (breadCrumbs != null) {
-      for (int i = 0; i < breadCrumbs.length; i++) {
-        BreadCrumb breadCrumb = breadCrumbs[i];
+      for (int i = 0; i < breadCrumbs!.length; i++) {
+        BreadCrumb breadCrumb = breadCrumbs![i];
         if (breadCrumb.text == null && breadCrumb.item != null) {
           if (breadCrumb.onTap == null) {
-            widgets.add(breadCrumb.item);
+            widgets.add(breadCrumb.item!);
           } else {
             widgets.add(MouseRegion(
               cursor: SystemMouseCursors.click,
@@ -186,9 +186,9 @@ class BreadCrumbs extends StatelessWidget {
 class BreadCrumb {
   final String text;
   final String route;
-  final IconData icon;
-  final Widget item;
-  final Function onTap;
+  final IconData? icon;
+  final Widget? item;
+  final GestureTapCallback? onTap;
 
   BreadCrumb(this.text, this.route, {this.icon, this.item, this.onTap});
 }