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/Data/PluginState.cs

@@ -0,0 +1,29 @@
+using System.Collections.Generic;
+using Jellyfin.Plugin.MediaCleaner.Models;
+
+namespace Jellyfin.Plugin.MediaCleaner.Data;
+
+public class PluginState
+{
+    private readonly object _lock = new();
+    private List<SeriesInfo> _seriesInfo = new List<SeriesInfo>
+    {
+        new SeriesInfo { SeriesName = "TestName", Id = System.Guid.NewGuid() }
+    };
+
+    public void AddSeriesInfo(SeriesInfo seriesInfo)
+    {
+        lock (_lock)
+        {
+            _seriesInfo.Add(seriesInfo);
+        }
+    }
+
+    public IEnumerable<SeriesInfo> GetSeriesInfo()
+    {
+        lock (_lock)
+        {
+            return _seriesInfo;
+        }
+    }
+}