Use png for storage

Jellyfin.Api/Controllers/ImageController.cs

@@ -1747,7 +1747,7 @@ namespace Jellyfin.Api.Controllers
             }
             else
             {
-                splashscreenPath = Path.Combine(_appPaths.DataPath, "splashscreen.webp");
+                splashscreenPath = Path.Combine(_appPaths.DataPath, "splashscreen.png");
                 if (!System.IO.File.Exists(splashscreenPath))
                 {
                     return NotFound();

Jellyfin.Drawing.Skia/SkiaEncoder.cs

@@ -496,7 +496,7 @@ namespace Jellyfin.Drawing.Skia
         public void CreateSplashscreen(IReadOnlyList<string> posters, IReadOnlyList<string> backdrops)
         {
             var splashBuilder = new SplashscreenBuilder(this);
-            var outputPath = Path.Combine(_appPaths.DataPath, "splashscreen.webp");
+            var outputPath = Path.Combine(_appPaths.DataPath, "splashscreen.png");
             splashBuilder.GenerateSplash(posters, backdrops, outputPath);
         }