feat(router): implement route permissions mapping

- Create a new file for defining route permissions based on user roles
- Establish a centralized mapping of dashboard user roles to permitted routes
- Include permissions for admin and publisher roles
- Utilize the existing Routes and DashboardUserRole enums

Author: fulleni

lib/router/route_permissions.dart

@@ -0,0 +1,22 @@
+import 'package:core/core.dart';
+import 'package:flutter_news_app_web_dashboard_full_source_code/router/routes.dart';
+
+/// A centralized mapping of dashboard user roles to their permitted routes.
+///
+/// This map is used by the router's redirect logic to enforce navigation
+/// restrictions based on the authenticated user's role.
+final Map<DashboardUserRole, Set<String>> routePermissions = {
+  // Admins have access to all major sections of the dashboard.
+  DashboardUserRole.admin: {
+    Routes.overviewName,
+    Routes.contentManagementName,
+    Routes.userManagementName,
+    Routes.appConfigurationName,
+  },
+  // Publishers have a more restricted access, focused on content creation
+  // and management.
+  DashboardUserRole.publisher: {
+    Routes.overviewName,
+    Routes.contentManagementName,
+  },
+};