perf(video): move tier scaling to ffmpeg

The frame pump now submits crop-sized BGRA frames; FFmpeg scales them to final tier dimensions. Bundled scaler benchmark: 300 608x1080 to 1080x1920 frames in 0.435s (scaler-only).

Reference: https://ffmpeg.org/ffmpeg-filters.html#scale-1

ViewModels/MainViewModel.Streaming.Operations.cs

@@ -422,6 +422,7 @@ public partial class MainViewModel : ViewModelBase
     {
         var url = _rtmpUrlProvider();
         var quality = OutputProfile.Resolve(SelectedQuality, QualityOptions, HasProOutput);
+        var compositor = BuildCompositorOptions();
         return new EncoderOptions
         {
             RtmpUrl = url ?? string.Empty,
@@ -430,6 +431,8 @@ public partial class MainViewModel : ViewModelBase
             RecordPath = _activeRecordPath,
             Width = quality.Width,
             Height = quality.Height,
+            InputWidth = compositor.OutputWidth,
+            InputHeight = compositor.OutputHeight,
             Fps = quality.Fps,
             BitrateKbps = (int)Math.Round(quality.Bitrate * 1000),
         };