show topics and summaries for spaces

lib/widgets/room_title.dart

@@ -0,0 +1,22 @@
+import "package:material_ui/material_ui.dart";
+
+/// A room or space's name, with its topic underneath if it has one, for app
+/// bars.
+class const RoomTitle(final String name, {final String? topic, super.key})
+    extends StatelessWidget {
+  @override
+  Widget build(BuildContext context) => Column(
+    crossAxisAlignment: .start,
+    children: [
+      Text(name, overflow: .ellipsis, maxLines: 1),
+      if (topic?.isNotEmpty == true)
+        Text(
+          topic!,
+          maxLines: 1,
+          overflow: .ellipsis,
+          style: Theme.of(context).textTheme.labelMedium
+              ?.copyWith(color: Theme.of(context).colorScheme.onSurfaceVariant),
+        ),
+    ],
+  );
+}