Show space hierarchies

Fixes #83

lib/helpers/extensions/show_leave_room_sheet.dart

@@ -0,0 +1,39 @@
+import "package:flutter_riverpod/flutter_riverpod.dart";
+import "package:material_ui/material_ui.dart";
+import "package:nexus/controllers/client.dart";
+import "package:nexus/helpers/extensions/show_adaptive_sheet.dart";
+import "package:nexus/helpers/extensions/with_progress_snackbar.dart";
+import "package:nexus/widgets/sheet_layout.dart";
+
+extension ShowLeaveRoomSheet on BuildContext {
+  /// Asks the user to confirm leaving the room, then leaves it.
+  Future<void> showLeaveRoomSheet(String roomId, {required String name}) =>
+      showAdaptiveSheet(
+        (context) => SheetLayout(
+          title: const Text("Leave Room"),
+          actions: [
+            TextButton(
+              onPressed: Navigator.of(context).pop,
+              child: const Text("Cancel"),
+            ),
+            TextButton(
+              onPressed: () {
+                final client = ProviderScope.containerOf(
+                  context,
+                ).read(ClientController.provider.notifier);
+                context.withProgressSnackbar(
+                  "Leaving $name...",
+                  () => client.leaveRoom(roomId),
+                );
+                Navigator.of(context).pop();
+              },
+              style: TextButton.styleFrom(
+                foregroundColor: Theme.of(context).colorScheme.error,
+              ),
+              child: const Text("Leave"),
+            ),
+          ],
+          children: [Text("Are you sure you want to leave \"$name\"?")],
+        ),
+      );
+}