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/navigationbar.dart

@@ -9,17 +9,17 @@ import 'breadcrumbs.dart';
 typedef OnBackPress();
 
 class MiniNavigationBar extends StatefulWidget implements PreferredSizeWidget {
-  final Key key;
+  final Key? key;
   final String title;
   final bool back;
   final bool toHome;
   final bool showMe;
-  final List<BreadCrumb> breadCrumbs;
-  final double breadCrumbHeight;
-  final Widget shoppingCart;
+  final List<BreadCrumb>? breadCrumbs;
+  final double? breadCrumbHeight;
+  final Widget? shoppingCart;
 
-  MiniNavigationBar({Key key, PreferredSizeWidget bottom, String title,
-    bool back, bool toHome, bool showMe, this.breadCrumbs,
+  MiniNavigationBar({Key? key, PreferredSizeWidget? bottom, String? title,
+    bool? back, bool? toHome, bool? showMe, this.breadCrumbs,
     this.breadCrumbHeight, this.shoppingCart})
       : key = key,
         preferredSize = breadCrumbHeight != null ? Size.fromHeight(kToolbarHeight + breadCrumbHeight) :
@@ -47,9 +47,9 @@ class MiniNavigationBarState extends State<MiniNavigationBar> {
       mobile: MobileNavigationBar(title: widget.title, back: widget.back,
         toHome: widget.toHome, showMe: widget.showMe,),
       tablet: DesktopNavigationBar(hasBack: widget.back,
-        breadCrumbs: widget.breadCrumbs, shoppingCart: widget.shoppingCart,),
+        breadCrumbs: widget.breadCrumbs ?? [], shoppingCart: widget.shoppingCart ?? const SizedBox.shrink(),),
       desktop: DesktopNavigationBar(hasBack: widget.back,
-        breadCrumbs: widget.breadCrumbs, shoppingCart: widget.shoppingCart,),
+        breadCrumbs: widget.breadCrumbs ?? [], shoppingCart: widget.shoppingCart ?? const SizedBox.shrink(),),
     );
   }