Fix CRT shader: add OpenCL capability check and scale_opencl syntax

- IsCrtShaderEnabled now guards on SupportsHwaccel("opencl"),
  SupportsFilter("program_opencl") and SupportsFilter("scale_opencl")
  so the filter is silently skipped instead of causing an FFmpeg error
  when OpenCL is unavailable
- Drop w=iw:h=ih from scale_opencl (iw/ih are not valid expressions in
  the OpenCL scale filter; omitting them defaults to input dimensions)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

MediaBrowser.Controller/MediaEncoding/EncodingHelper.cs

@@ -3716,7 +3716,10 @@ namespace MediaBrowser.Controller.MediaEncoding
         {
             return state.BaseRequest.StreamOptions.TryGetValue("crtShader", out var val)
                 && string.Equals(val, "true", StringComparison.OrdinalIgnoreCase)
-                && File.Exists(Path.Combine(AppContext.BaseDirectory, "Resources", "Shaders", "crt_lottes.cl"));
+                && File.Exists(Path.Combine(AppContext.BaseDirectory, "Resources", "Shaders", "crt_lottes.cl"))
+                && _mediaEncoder.SupportsHwaccel("opencl")
+                && _mediaEncoder.SupportsFilter("program_opencl")
+                && _mediaEncoder.SupportsFilter("scale_opencl");
         }
 
         private string GetCrtEscapedShaderPath()
@@ -3751,10 +3754,10 @@ namespace MediaBrowser.Controller.MediaEncoding
 
             return
             [
-                "scale_opencl=w=iw:h=ih:format=rgba",
+                "scale_opencl=format=rgba",
                 FormattableString.Invariant(
                     $"program_opencl=source={escapedPath}:kernel=crt_lottes:build_opts='{buildOpts}'"),
-                "scale_opencl=w=iw:h=ih:format=nv12"
+                "scale_opencl=format=nv12"
             ];
         }