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

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

web/guest.html

@@ -5,6 +5,7 @@
 <body>
 <header><h1>JohnFeed</h1><span id="conn" class="pill">connecting…</span></header>
 <div id="fatal" class="banner hidden"></div>
+<div id="tally" class="tallybar off" role="status" aria-live="polite">Off air</div>
 <main class="grid">
   <section class="card" id="audio">
     <h2>Audio</h2>