feat: check every subscription in the background and add the posts page

app/lib/application/internal_pages.dart

@@ -3,10 +3,12 @@ import '../l10n/strings.dart';
 import '../mews/document.dart';
 import 'controllers/reader_settings_controller.dart'
     show ReaderSettingsController;
+import 'controllers/subscriptions_controller.dart';
 import 'pages/bookmarks_page.dart';
 import 'pages/history_page.dart';
 import 'pages/hub_page.dart';
 import 'pages/mews_urls.dart';
+import 'pages/posts_page.dart';
 import 'pages/settings_page.dart';
 import 'pages/subscriptions_page.dart';
 
@@ -17,13 +19,16 @@ class InternalPages {
   InternalPages({
     required MewsDatabase db,
     required ReaderSettingsController settings,
+    required SubscriptionsController subscriptions,
     required Strings strings,
   })  : _db = db,
         _settings = settings,
+        _subscriptions = subscriptions,
         _strings = strings;
 
   final MewsDatabase _db;
   final ReaderSettingsController _settings;
+  final SubscriptionsController _subscriptions;
   final Strings _strings;
 
   /// Whether [url] is one of the internal pages.
@@ -34,7 +39,12 @@ class InternalPages {
     // Internal addresses are opaque, so the page name is the path, not a host.
     final uri = Uri.parse(MewsUrls.canonical(url));
     return switch (uri.path) {
-      'hub' => buildHubPage(uri, db: _db, strings: _strings),
+      'hub' => buildHubPage(uri,
+          db: _db, subscriptions: _subscriptions, strings: _strings),
+      'posts' => buildPostsPage(uri,
+          db: _db,
+          strings: _strings,
+          refreshing: _subscriptions.refreshing.value),
       'bookmarks' => buildBookmarksPage(uri, db: _db, strings: _strings),
       'subscriptions' => buildSubscriptionsPage(uri, db: _db, strings: _strings),
       'history' => buildHistoryPage(uri, db: _db, strings: _strings),