feat: add showUserAvatar option to video player and embed UI

- Added 'showUserAvatar' parameter to control author avatar visibility in embed info overlay
- Implemented UI toggle in MediaShareEmbed for the 'showUserAvatar' option
- Propagated 'showUserAvatar' through EmbedPage, VideoViewer, and VideoJSEmbed
- Updated test iframe index with all 8 combinations of showTitle, showRelated, and showUserAvatar

frontend/src/static/js/pages/EmbedPage.tsx

@@ -63,6 +63,7 @@ export const EmbedPage: React.FC = () => {
             const urlParams = new URLSearchParams(window.location.search);
             const showTitle = urlParams.get('showTitle') !== '0';
             const showRelated = urlParams.get('showRelated') !== '0';
+            const showUserAvatar = urlParams.get('showUserAvatar') !== '0';
             return (
               <VideoViewer 
                 data={MediaPageStore.get('media-data')} 
@@ -70,6 +71,7 @@ export const EmbedPage: React.FC = () => {
                 containerStyles={containerStyles} 
                 showTitle={showTitle}
                 showRelated={showRelated}
+                showUserAvatar={showUserAvatar}
               />
             );
           }}