saveVideoToGallery
Saves what an export wrote into the platform's video gallery.
Android inserts it into MediaStore, Apple adds it to the photo library and the JVM copies it into the user's videos directory. An iOS app declares NSPhotoLibraryAddUsageDescription in its plist, and an Android app that still runs below API 29 declares WRITE_EXTERNAL_STORAGE with maxSdkVersion="28", since FileKit's own artifact declares neither. Nothing is needed on API 29 and up.
Return
Result.failure when the save does not go through. It carries an IllegalStateException for MediaSink.Temporary, which is a request rather than a location, so read the resolved path off ExportStatus.Success.output instead. A MediaSink.Uri this platform cannot parse carries an IllegalArgumentException, and anything else is FileKit's own exception.
Parameters
Where the export wrote, taken whole so a content:// destination stays one.
The name the gallery entry takes, defaulting to the written file's own name.