Initial commit: private Texas Hold'em ring game site (lobby + table stub)

- 6-digit access key gate with long-lived HttpOnly cookie, brute-force limits
- Lobby with saved player name and live table list
- Table creation (name, starting stack, blinds, blind timer)
- Table play screen stub (seats, button/SB/BB, phase, blinds, timer)
- Security hardening: strict CSP, origin checks, host pinning, input sanitizing

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

public/lobby.html

@@ -0,0 +1,34 @@
+<!doctype html>
+<html lang="ja">
+<head>
+  <meta charset="utf-8">
+  <meta name="viewport" content="width=device-width, initial-scale=1, viewport-fit=cover">
+  <meta name="theme-color" content="#24493b">
+  <meta name="robots" content="noindex, nofollow">
+  <title>Hold'em Night</title>
+  <link rel="stylesheet" href="/assets/style.css">
+</head>
+<body>
+  <main class="wrap">
+    <div class="logo">Hold'em<br>Night<small>PRIVATE CLUB</small></div>
+
+    <label for="name">あなたの名前</label>
+    <input id="name" type="text" maxlength="12" placeholder="例: とらのすけ" autocomplete="nickname">
+    <div class="error-text" id="name-error"></div>
+
+    <button id="create" class="btn btn-orange btn-block mt-4" type="button">＋ テーブルを作成</button>
+
+    <div class="section-title">
+      <span>開催中のテーブル</span>
+      <span class="sub" id="count"></span>
+    </div>
+    <div class="table-list" id="list">
+      <div class="empty">読み込み中…</div>
+    </div>
+  </main>
+
+  <script src="/socket.io/socket.io.js"></script>
+  <script src="/assets/common.js"></script>
+  <script src="/assets/lobby.js"></script>
+</body>
+</html>