Two-stage mount splits the propagation map's first paint: the static
HTTP render still fetches scores synchronously so SEO/noscript shipping
gets real data baked into `data-scores`, but the websocket-connected
mount defers the potentially-slow fetch to `start_async/3`. Chrome
paints immediately; scores stream in via an `update_scores` push_event
once `handle_async(:initial_scores, ...)` resolves.
A small overlay (spinner on `:loading`, retry button on `:failed`)
uses `<.async_result>` so users can see state and recover from a
transient fetch error.
Graham McIntire
ef4e63aef4