Add custom OG thumbnails for shared conversations
Shared conversation URLs (/r/[id]) now generate dynamic thumbnails
showing the conversation topic, so social media previews display
meaningful content instead of the generic HuggingChat image.
- Add thumbnail.png endpoint using Satori+Resvg (same as model thumbnails)
- Convert /r/[id] from redirect-only to SSR page with OG meta tags
- Redirect logic moved to client-side onMount (crawlers see OG tags)
- Exclude /r/ paths from layout default OG tags to prevent duplicates
https://claude.ai/code/session_01TWxkFGJP7HbWyUHpBwx26N
