Implement Texas Hold'em play: dealing, betting, side pots, showdown

- Hand engine (server/hand.js): crypto-shuffled deck kept server-side,
  blinds (heads-up button = SB), min-raise rules incl. incomplete all-in,
  uncalled bet refunds, side pots, split pots, all-in runout
- Hand evaluator (server/cards.js) and node:test suite (npm test)
- Table flow: hands auto-continue after host START, 30s action clock
  (timeout = check/fold + sit out), sit out / sit in, rebuy, mid-hand leave
  folds and keeps the seat reserved until the hand ends, pause freezes all clocks
- Only each player's own hole cards are sent until a showdown/runout reveal;
  all actions validated server-side
- Play UI: board, hole cards, bets, action tags, turn timer, raise panel with
  presets, showdown results with winning cards highlighted, compact 7+ layout
- Remove the host crown and the temporary "next phase" control

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

server/config.js

@@ -53,6 +53,16 @@ module.exports = {
   // 誰も接続していないテーブルを削除するまでの時間
   EMPTY_TABLE_TTL_MS: 30 * 60 * 1000,
 
+  // 1手の持ち時間。過ぎると自動でチェック/フォールドして離席扱い
+  ACTION_TIME_MS: 30 * 1000,
+  // オールインで残りのカードをめくる間隔
+  RUNOUT_STEP_MS: 1500,
+  // ハンド終了後、次のハンドまで結果を表示する時間
+  SHOWDOWN_MS: 5000,
+  FOLD_WIN_MS: 2500,
+  // 参加者が2人揃ってから次のハンドを始めるまで
+  NEXT_HAND_DELAY_MS: 2000,
+
   // 鍵入力のブルートフォース対策
   // IP（IPv6 は /64 単位）ごと: WINDOW 内で MAX_FAILURES 回まで
   AUTH_MAX_FAILURES: 5,