feat(video): add path-string loader variant

UniverSR Load Video Audio (Path) mirrors FoleyTuneVideoLoader: takes an
absolute video_path (for files outside input/) and outputs the same
(UNIVERSR_VIDEO, AUDIO). Shared load body factored into _load_video_audio;
registered for the inline preview (post-run) in the web extension.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

web/js/UniverSRVideo.js

@@ -150,6 +150,9 @@ app.registerExtension({
             addVideoPreview(nodeType);
             addUploadWidget(nodeType);
         }
+        if (nodeData?.name === "UniverSRLoadVideoAudioPath") {
+            addVideoPreview(nodeType);
+        }
         if (nodeData?.name === "UniverSRVideoCombiner") {
             addVideoPreview(nodeType);
         }