Add CPU opponents and a table type selector (cash only / friends / CPU)

- Create screen: choose キャッシュオンリー (real cards, chips only), 友人戦
  (server deals and settles) or CPU戦 (友人戦 plus 1–8 CPU players); replaces
  the card toggle. The lobby shows each table's type
- Poker AI written from scratch (server/ai.js, no libraries): fast 7-card
  evaluator (checked against bestHand), Monte Carlo equity, and decisions from
  hand rank, pot odds, raise count, opponents and a per-CPU style (aggression,
  bluff rate); continuation bets via the last aggressor. It never sees other
  players' hole cards
- CPU seats: think time of 0.7–1.8s (faster when no human is left in the hand),
  automatic rebuy, never the host, no new hand unless a human is playing,
  re-think after pause
- Play UI: robot avatars and a "考えています…" status for CPU turns
- Tests for the evaluator, equity, legality of AI actions and CPU tables

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

server/index.js

@@ -6,7 +6,7 @@ const express = require('express');
 const { Server } = require('socket.io');
 const config = require('./config');
 const auth = require('./auth');
-const { TableManager } = require('./tables');
+const { TableManager, MODES } = require('./tables');
 
 const PUBLIC = path.join(__dirname, '..', 'public');
 // 管理者専用のファイル（public の外に置き、管理者の Cookie があるときだけ返す）
@@ -114,7 +114,8 @@ app.post('/api/tables', (req, res) => {
   const bigBlind = b.bigBlind;
   const blindTimerEnabled = b.blindTimerEnabled === true;
   const blindIntervalMin = b.blindIntervalMin;
-  const cardsEnabled = b.cardsEnabled === true;
+  const mode = b.mode;
+  const cpuCount = b.cpuCount;
   const hostToken = cleanToken(b.token);
 
   if (tables.tables.size >= config.MAX_TABLES) return res.status(429).json({ error: 'テーブル数が上限に達しています' });
@@ -124,6 +125,10 @@ app.post('/api/tables', (req, res) => {
   if (!intIn(smallBlind, 1, startingStack)) return res.status(400).json({ error: 'SBが不正です' });
   if (!intIn(bigBlind, smallBlind, startingStack)) return res.status(400).json({ error: 'BBはSB以上・開始スタック以下にしてください' });
   if (blindTimerEnabled && !intIn(blindIntervalMin, 1, 240)) return res.status(400).json({ error: 'インターバルは1〜240分で入力してください' });
+  if (!MODES.includes(mode)) return res.status(400).json({ error: 'テーブルの種類が不正です' });
+  if (mode === 'cpu' && !intIn(cpuCount, 1, config.MAX_SEATS - 1)) {
+    return res.status(400).json({ error: `CPU の人数は1〜${config.MAX_SEATS - 1}人にしてください` });
+  }
   if (!hostToken) return res.status(400).json({ error: 'プレイヤーIDがありません' });
 
   const table = tables.create({
@@ -133,7 +138,8 @@ app.post('/api/tables', (req, res) => {
     bigBlind,
     blindTimerEnabled,
     blindIntervalMin: blindTimerEnabled ? blindIntervalMin : 10,
-    cardsEnabled,
+    mode,
+    cpuCount: mode === 'cpu' ? cpuCount : 0,
     hostToken,
   });
   broadcastLobby();