Add guest tally (on air / off air) and host connection warning

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

web/host.html

@@ -13,6 +13,9 @@
     </div>
     <p class="muted small">A new link ends the current session and clears chat. Old links stop working.</p>
     <h2>Guest</h2>
+    <div class="row"><button id="tally" class="tally" title="Shows ON AIR / Off air on the guest's page. Does not change any audio.">Off air</button>
+      <span class="muted small">Guest's tally light - sign only, no audio change</span></div>
+    <div id="warn" class="warnbox hidden" role="status"></div>
     <div id="guest" class="big">No guest connected</div>
     <div id="callinfo" class="muted small"></div>
     <div class="meter"><span>Guest &rarr; show</span><div class="bar"><i id="mIn"></i></div><b id="dIn"></b></div>