feat(router): add archived content routes and placeholders

- Remove ArchivedContentPage import and route
- Add separate routes for archived headlines, topics, and sources
- Implement placeholder pages for new archived content routes

Author: fulleni

lib/router/router.dart

@@ -17,7 +17,6 @@ import 'package:flutter_news_app_web_dashboard_full_source_code/content_manageme
 import 'package:flutter_news_app_web_dashboard_full_source_code/content_management/view/edit_headline_page.dart';
 import 'package:flutter_news_app_web_dashboard_full_source_code/content_management/view/edit_source_page.dart';
 import 'package:flutter_news_app_web_dashboard_full_source_code/content_management/view/edit_topic_page.dart';
-import 'package:flutter_news_app_web_dashboard_full_source_code/content_management/view/archived_content_page.dart';
 import 'package:flutter_news_app_web_dashboard_full_source_code/dashboard/view/dashboard_page.dart';
 import 'package:flutter_news_app_web_dashboard_full_source_code/router/routes.dart';
 import 'package:flutter_news_app_web_dashboard_full_source_code/settings/view/settings_page.dart';
@@ -198,9 +197,22 @@ GoRouter createRouter({
                     },
                   ),
                   GoRoute(
-                    path: Routes.archivedContent,
-                    name: Routes.archivedContentName,
-                    builder: (context, state) => const ArchivedContentPage(),
+                    path: Routes.archivedHeadlines,
+                    name: Routes.archivedHeadlinesName,
+                    builder: (context, state) =>
+                        const Placeholder(),
+                  ),
+                  GoRoute(
+                    path: Routes.archivedTopics,
+                    name: Routes.archivedTopicsName,
+                    builder: (context, state) =>
+                        const Placeholder(),
+                  ),
+                  GoRoute(
+                    path: Routes.archivedSources,
+                    name: Routes.archivedSourcesName,
+                    builder: (context, state) =>
+                        const Placeholder(),
                   ),
                 ],
               ),