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/Controllers/StateController.cs

@@ -0,0 +1,22 @@
+using Jellyfin.Plugin.MediaCleaner.Data;
+using Jellyfin.Plugin.MediaCleaner.Models;
+using Microsoft.AspNetCore.Mvc;
+
+namespace Jellyfin.Plugin.MediaCleaner.Controllers;
+
+[Route("mediacleaner/state")]
+public class StateController : Controller
+{
+    private readonly PluginState _state;
+    public StateController(PluginState state) => _state = state;
+
+    [HttpGet]
+    public IActionResult Get() => Ok(_state.GetSeriesInfo());
+
+    [HttpPost("add")]
+    public IActionResult AddSeriesInfo([FromBody] SeriesInfo seriesInfo)
+    {
+        _state.AddSeriesInfo(seriesInfo);
+        return Ok();
+    }
+}