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/key.html

@@ -0,0 +1,33 @@
+<!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>
+
+    <form id="form" class="card" autocomplete="off">
+      <h2 class="key-title">参加キーを入力</h2>
+      <p class="hint key-hint">オーナーから教えてもらった6桁の数字</p>
+      <div class="key-inputs" id="digits">
+        <input type="tel" inputmode="numeric" aria-label="1桁目" autocomplete="one-time-code">
+        <input type="tel" inputmode="numeric" aria-label="2桁目">
+        <input type="tel" inputmode="numeric" aria-label="3桁目">
+        <input type="tel" inputmode="numeric" aria-label="4桁目">
+        <input type="tel" inputmode="numeric" aria-label="5桁目">
+        <input type="tel" inputmode="numeric" aria-label="6桁目">
+      </div>
+      <div class="error-text text-center" id="error"></div>
+      <button class="btn btn-orange btn-block mt-8" id="submit" type="submit">入室する</button>
+    </form>
+  </main>
+  <script src="/assets/common.js"></script>
+  <script src="/assets/key.js"></script>
+</body>
+</html>