test(live): 7 tests for the Live polish work

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]>

resources/views/live/watch.blade.php

@@ -291,6 +291,7 @@
 @endsection
 
 @section('scripts')
+@unless($isEnded)
 <script>
 (function () {
     'use strict';
@@ -496,4 +497,5 @@
     window.addEventListener('pagehide', teardown);
 })();
 </script>
+@endunless
 @endsection