Add room preview dialog

Closes #79

lib/widgets/room_summary_dialog.dart

@@ -0,0 +1,72 @@
+import "package:fast_immutable_collections/fast_immutable_collections.dart";
+import "package:hooks_riverpod/hooks_riverpod.dart";
+import "package:material_ui/material_ui.dart";
+import "package:nexus/widgets/avatar_or_hash.dart";
+import "package:nexus/widgets/expandable_image.dart";
+import "package:nexus/widgets/linkified_text.dart";
+import "package:nexus/models/room_summary.dart";
+
+class const RoomSummaryDialog(
+  final RoomSummary summary, {
+  final IList<Widget> extraActions = const IList.empty(),
+  super.key,
+}) extends ConsumerWidget {
+  @override
+  Widget build(BuildContext context, WidgetRef ref) => AlertDialog(
+    constraints: .loose(.fromWidth(400)),
+    scrollable: true,
+    contentPadding: EdgeInsets.all(24).copyWith(top: 8),
+    title: Row(
+      spacing: 12,
+      mainAxisSize: .min,
+      children: [
+        if (summary.avatarUrl != null)
+          ExpandableImage(
+            summary.avatarUrl == null ? null : .new(mxc: summary.avatarUrl!),
+            child: AvatarOrHash(
+              summary.avatarUrl,
+              summary.name ?? "Unnamed Room",
+              height: 64,
+              fallback: Icon(Icons.numbers),
+            ),
+          ),
+        Expanded(
+          child: Text(
+            summary.name ?? summary.canonicalAlias ?? summary.roomId,
+            overflow: .ellipsis,
+            maxLines: 3,
+          ),
+        ),
+      ],
+    ),
+    content: Column(
+      children: [
+        ListTile(
+          title: Text("${summary.joinedMembers} members"),
+          leading: Icon(Icons.people),
+        ),
+        ListTile(
+          title: SelectableText(summary.canonicalAlias ?? summary.roomId),
+          leading: Icon(Icons.numbers),
+        ),
+
+        if (summary.topic != null)
+          ListTile(
+            isThreeLine: true,
+            subtitle: LinkifiedText(
+              summary.topic!,
+              style: Theme.of(context).textTheme.bodyLarge?.copyWith(
+                color: Theme.of(context).colorScheme.onSurfaceVariant,
+              ),
+            ),
+            leading: Icon(Icons.info),
+          ),
+      ],
+    ),
+
+    actions: [
+      TextButton(onPressed: Navigator.of(context).pop, child: Text("Cancel")),
+      ...extraActions,
+    ],
+  );
+}