Managed to figure out how to use javascript on the plugin page by utilizing data-controller as found in other repos. Unsure how this is used, but appears to be how you can attach a js file to a div. Also implemented a basic state api to build off of in future.

Jellyfin.Plugin.MediaCleaner/PluginServiceRegistrator.cs

@@ -0,0 +1,13 @@
+using Jellyfin.Plugin.MediaCleaner.Data;
+using MediaBrowser.Controller;
+using MediaBrowser.Controller.Plugins;
+using Microsoft.Extensions.DependencyInjection;
+
+namespace Jellyfin.Plugin.MediaCleaner;
+public class PluginServiceRegistrator : IPluginServiceRegistrator
+{
+    public void RegisterServices(IServiceCollection serviceCollection, IServerApplicationHost applicationHost)
+    {
+        serviceCollection.AddSingleton<PluginState>();
+    }
+}