feat(useragent): settled on routing architecture

useragent/lib/screens/dashboard.dart

@@ -0,0 +1,42 @@
+import 'package:arbiter/router.gr.dart';
+import 'package:auto_route/auto_route.dart';
+import 'package:flutter/material.dart';
+import 'package:flutter_adaptive_scaffold/flutter_adaptive_scaffold.dart';
+
+const breakpoints = MaterialAdaptiveBreakpoints();
+
+final routes = [AboutRoute(), CalcRoute()];
+
+@RoutePage()
+class DashboardRouter extends StatelessWidget {
+  const DashboardRouter({super.key});
+
+  @override
+  Widget build(BuildContext context) {
+    return AutoTabsRouter(
+      routes: routes,
+      transitionBuilder: (context, child, animation) => FadeTransition(
+        opacity: animation,
+        // the passed child is technically our animated selected-tab page
+        child: child,
+      ),
+      builder: (context, child) {
+        final tabsRouter = AutoTabsRouter.of(context);
+        final currentActive = tabsRouter.activeIndex;
+        return AdaptiveScaffold(
+          destinations: [
+            NavigationDestination(icon: Icon(Icons.book), label: "About"),
+            NavigationDestination(icon: Icon(Icons.calculate), label: "Calc"),
+          ],
+          body: (ctx) => child,
+          onSelectedIndexChange: (index) {
+            tabsRouter.navigate(routes[index]);
+          },
+          selectedIndex: currentActive,
+          transitionDuration: Duration(milliseconds: 800),
+        internalAnimations: true,          
+        );
+      },
+    );
+  }
+}