fix: include image_url in playlist SSR data for og:image (#507)

the SSR fallback object was missing image_url from playlistMeta,
causing og:image to be undefined in link previews even when the
playlist has cover art.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude <noreply@anthropic.com>

authored by zzstoatzz.io Claude and committed by GitHub b4bc517f da7d9540

Changed files
+1
frontend
src
routes
playlist
[id]
+1
frontend/src/routes/playlist/[id]/+page.ts
··· 23 23 owner_did: serverData?.playlistMeta?.owner_did ?? '', 24 24 owner_handle: serverData?.playlistMeta?.owner_handle ?? '', 25 25 track_count: serverData?.playlistMeta?.track_count ?? 0, 26 + image_url: serverData?.playlistMeta?.image_url, 26 27 show_on_profile: serverData?.playlistMeta?.show_on_profile ?? false, 27 28 atproto_record_uri: serverData?.playlistMeta?.atproto_record_uri ?? '', 28 29 created_at: serverData?.playlistMeta?.created_at ?? '',