feat: add a hub for the client's own pages and gate mews:do action links

app/lib/database/database.dart

@@ -91,6 +91,19 @@ class MewsDatabase extends _$MewsDatabase {
     return row?.url;
   }
 
+  /// Row counts for the hub, so it can say what each page holds without
+  /// reading every row.
+  Future<int> countHistory() => _countOf(historyItems, historyItems.id);
+  Future<int> countBookmarks() => _countOf(bookmarks, bookmarks.id);
+  Future<int> countSubscriptions() => _countOf(subscriptions, subscriptions.id);
+
+  Future<int> _countOf(ResultSetImplementation<HasResultSet, dynamic> table,
+      GeneratedColumn<int> column) async {
+    final total = column.count();
+    final query = selectOnly(table)..addColumns([total]);
+    return (await query.getSingle()).read(total) ?? 0;
+  }
+
   /// The most recent external visits, newest first.
   Future<List<HistoryItem>> recentVisits({int limit = 50}) async {
     final query = (select(historyItems)