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/hand.js

@@ -29,6 +29,10 @@ class Hand {
     this.pot = 0; // 前のストリートまでに集めた額
     this.currentBet = 0;
     this.minRaise = bb;
+    this.raises = 0; // このストリートのベット・レイズの回数（CPU の判断用）
+    this.actions = 0; // アクションの通し番号（CPU の手番の管理用）
+    this.aggressor = null; // このストリートで最後にベット・レイズした席（CPU の判断用）
+    this.prevAggressor = null; // 前のストリートで最後にベット・レイズした席
     this.toAct = null;
     this.finished = false;
     this.showdown = false;
@@ -75,6 +79,11 @@ class Hand {
     return this.list.filter((p) => !p.folded);
   }
 
+  // 前のストリートまでのポット + このストリートのベット
+  get potTotal() {
+    return this.pot + this.list.reduce((sum, p) => sum + p.bet, 0);
+  }
+
   put(p, amount) {
     const s = this.seats[p.seat];
     s.stack -= amount;
@@ -163,9 +172,11 @@ class Hand {
       const raiseSize = amount - this.currentBet;
       this.put(p, amount - p.bet);
       p.last = { type: o.isBet ? 'BET' : 'RAISE', amount };
+      this.aggressor = seat;
       if (raiseSize >= this.minRaise) {
         // 正規のレイズ: 他の人はもう一度アクションできる
         this.minRaise = raiseSize;
+        this.raises++;
         for (const q of this.list) if (q !== p) q.acted = false;
       }
       // 足りないオールインのレイズはアクション済みの人に再レイズ権を与えない
@@ -175,6 +186,7 @@ class Hand {
     }
     if (p.allIn) p.last = { type: 'ALLIN', amount: p.bet };
     p.acted = true;
+    this.actions++;
     this.setNextActor(seat);
     return null;
   }
@@ -225,6 +237,9 @@ class Hand {
     if (this.live().length === 1) return this.finishFoldWin();
     this.currentBet = 0;
     this.minRaise = this.bb;
+    this.raises = 0;
+    this.prevAggressor = this.aggressor;
+    this.aggressor = null;
 
     const noMoreBetting = this.live().filter((p) => !p.allIn).length < 2;
     if (!this.cards) {
@@ -365,7 +380,7 @@ class Hand {
       runout: this.runout,
       street: this.street,
       pot: this.pot,
-      potTotal: this.pot + this.list.reduce((sum, p) => sum + p.bet, 0),
+      potTotal: this.potTotal,
       currentBet: this.currentBet,
       button: this.button,
       sbSeat: this.sbSeat,