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>

public/assets/style.css

@@ -255,6 +255,29 @@ input.invalid { border-color: var(--red); }
 .switch input:checked + span::before { transform: translateX(22px); background: #fff; }
 .switch input:focus-visible + span { outline: 2px solid var(--gold); }
 
+/* 選択肢を横に並べたラジオボタン（テーブルの種類・CPU の人数） */
+.segmented { display: grid; grid-auto-flow: column; grid-auto-columns: 1fr; gap: 6px; }
+.segmented label { margin: 0; display: block; color: var(--text); }
+.segmented input { position: absolute; opacity: 0; width: 0; height: 0; }
+.segmented span {
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  text-align: center;
+  min-height: 52px;
+  padding: 6px 4px;
+  border-radius: 12px;
+  background: var(--input);
+  border: 2px solid transparent;
+  font-weight: 800;
+  font-size: 14px;
+  line-height: 1.2;
+  cursor: pointer;
+}
+.segmented input:checked + span { background: rgba(246, 199, 68, 0.15); border-color: var(--gold); color: var(--gold); }
+.segmented input:focus-visible + span { outline: 2px solid var(--gold); outline-offset: 2px; }
+.segmented.numbers span { min-height: 40px; font-size: 15px; }
+
 .unit-input { position: relative; }
 .unit-input input { padding-right: 56px; }
 .unit-input .unit {
@@ -400,6 +423,7 @@ body.table-page {
 }
 .avatar svg { width: 28px; height: 28px; fill: #fff; }
 .seat.me .avatar { background: #d35400; border-color: var(--gold); }
+.seat.bot .avatar { background: #3d4a6b; border-color: #8fa2d6; }
 .seat.offline .avatar { opacity: 0.45; }
 .nameplate {
   margin-top: -10px;