fix: suppress unhandled promise rejections from fire-and-forget useEffect loads

useAsync re-throws errors after storing them in state — correct for awaited
callers but causes unhandled rejections when load() is called without .catch()
in useEffects. The error is already captured in AsyncState.Error so the
re-throw provides no additional value in these fire-and-forget patterns.

Fixes JAVASCRIPT-REACT-M (Sentry: Media download failed: 401 Unauthorized)

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

src/app/components/message/content/VideoContent.tsx

@@ -106,7 +106,7 @@ export const VideoContent = as<'div', VideoContentProps>(
     };
 
     useEffect(() => {
-      if (autoPlay) loadSrc();
+      if (autoPlay) void loadSrc().catch(() => undefined);
     }, [autoPlay, loadSrc]);
 
     return (