guestlink v1: self-hosted guest line (Cleanfeed replacement)

Go + Pion + libopus. One guest, live audio both ways, anonymous chat.
README for this version was not preserved; see the next commit.

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

web/guest.html

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+<!doctype html>
+<html lang="en"><head><meta charset="utf-8"><meta name="viewport" content="width=device-width,initial-scale=1">
+<meta name="robots" content="noindex">
+<title>MMO Guest Line</title><link rel="stylesheet" href="/static/style.css"></head>
+<body>
+<header><h1>MMO Guest Line</h1><span id="conn" class="pill">connecting…</span></header>
+<div id="fatal" class="banner hidden"></div>
+<main class="grid">
+  <section class="card" id="audio">
+    <h2>Audio</h2>
+    <label class="field">Your name in chat <span class="muted">(optional - leave blank to stay anonymous)</span>
+      <input id="name" maxlength="40" placeholder="Guest" autocomplete="off"></label>
+    <label class="field">Microphone <select id="mic"><option value="">Default microphone</option></select></label>
+    <label class="field" id="outwrap">Headphones / output <select id="out"><option value="">Default output</option></select></label>
+    <label class="check"><input type="checkbox" id="headphones" checked> I'm wearing headphones <span class="muted">(best quality; untick only if you must use speakers)</span></label>
+    <div class="row">
+      <button id="join" class="primary">Join the show</button>
+      <button id="mute" class="hidden">Mute mic</button>
+      <button id="leave" class="hidden danger">Leave</button>
+    </div>
+    <div id="callstate" class="muted">Not connected to audio.</div>
+    <div class="meter"><span>Your mic</span><div class="bar"><i id="mMic"></i></div></div>
+    <div class="meter"><span>The show</span><div class="bar"><i id="mShow"></i></div></div>
+    <audio id="player" autoplay></audio>
+  </section>
+  <section class="card chat">
+    <h2>Chat with the host</h2>
+    <div id="log" class="log" aria-live="polite"></div>
+    <form id="chatform" class="row"><textarea id="msg" rows="2" maxlength="1000" placeholder="Type a message… (Enter to send)"></textarea><button class="primary">Send</button></form>
+  </section>
+</main>
+<script src="/static/common.js"></script>
+<script src="/static/guest.js"></script>
+</body></html>