Covers Private visibility acceptance, ended-state Watch page shows
"Stream ended" (and omits the "Waiting for the broadcast" placeholder
from the connection JS), channel-name link resolves to the user's
channel URL, chat poll returns messages newer than ?since=, chat send
rejects guests (401), chat send rejects offline streams (422), and
private-stream chat 404s for non-owners.
Also broadens LiveStream::isWatchableBy to keep public/unlisted
streams permalinked after they end — viewers now see the Stream Ended
card and the Watch Replay CTA instead of a hard 404.
Co-Authored-By: Claude Opus 4.7 (1M context) <[email protected]>
