master but no browser-playable proxy
Previously the player's "Retry processing" button only appeared for
assets in status='error'. Old recorder captures (e.g. the archived
'sRT Test_…' clips from May) live as status='archived' or 'ready' with
original_s3_key set but proxy_s3_key null. The /stream endpoint
correctly returned {url: null, reason: 'no_proxy'} for those, but the
player just showed "Preview not yet available" with no path forward —
which reads as "ingest worked, won't play, no idea why."
Two changes:
1) Capture {reason, has_source} from /stream so the UI can tell why
playback isn't available.
2) Render a "Generate proxy" button (using the existing
POST /assets/:id/retry endpoint, which the backend now accepts for
any asset with original_s3_key but no proxy_s3_key) whenever the
stream lookup returned no_proxy and the source exists. Original
error-status retry path is preserved.
Closes the visible half of #1 — the user can now self-recover proxy-
less clips from the library without DB surgery.