Channel/account avatars come from Google's image CDNs (yt3.ggpht.com,
lh3.googleusercontent.com). On a feed page dozens load at once; the CDN
rate-limits the referrer-bearing burst (429), so a random subset rendered the
browser's broken-image icon (the URLs themselves are valid — verified 200).
Add a shared <Avatar> that sets referrerPolicy="no-referrer" (which the CDNs
serve without throttling) and falls back to a neutral initial placeholder on
error instead of the broken-image icon. Use it for video-card, player, channel
manager, header and settings avatars.
