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]>

app/Models/LiveStream.php

@@ -124,7 +124,15 @@ class LiveStream extends Model
             return true;
         }
 
-        return $this->isLive() && in_array($this->visibility, ['public', 'unlisted'], true);
+        // Visibility first — private streams stay owner-only no matter what.
+        if (! in_array($this->visibility, ['public', 'unlisted'], true)) {
+            return false;
+        }
+
+        // Live streams are watchable while they're on; ended streams remain
+        // permalinked so viewers see "Stream ended" and the replay CTA
+        // instead of a hard 404.
+        return $this->isLive() || $this->status === self::STATUS_ENDED;
     }
 
     /* ---------------- Publish credential ---------------- */