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>

.env.example

@@ -0,0 +1,6 @@
+# .env にコピーして値を設定する（chmod 600 推奨）
+ACCESS_KEY=000000
+PORT=4671
+# HOST=127.0.0.1
+# 本番のみ設定（ローカル開発では設定しない）
+# PUBLIC_ORIGIN=https://poker.kanawo.net