Give CPUs distinct personalities built on different poker libraries

Each CPU now thinks with one of four engines, each backed by a different
published library (pinned versions):

- montecarlo (@pokertools/evaluator): the existing balanced Monte Carlo
  equity player, moved to server/bots/montecarlo.js.
- calculator (poker-calculations): the library's decideAction over the
  table state; push/fold below 12BB via its jam breakeven equity.
  Skipped automatically if the native addon cannot load.
- range (poker-utils): tight player; preflop by hand-strength percentile,
  postflop equity vs an estimated opponent range, bluffs only when
  alpha/bluffEV say they pay.
- madehand (pokersolver): loose, sticky player that only looks at the
  made hand and draws.

server/ai.js assigns a mix of engines per table (makeStyles), falls back
to the Monte Carlo engine on errors, and legalizes every decision.
The engine and its parameters stay server-side; players cannot tell
which library a CPU uses. Tests cover every engine and the no-leak rule.

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

test/engine.test.js

@@ -708,6 +708,76 @@ test('CPU: どんな状況でも正しいアクションを返す', () => {
   assert.ok(actions > 300, `actions=${actions}`);
 });
 
+test('CPU: どの思考（ライブラリ）も自分で正しいアクションを決める', () => {
+  const brains = ai.availableBrains();
+  // 少なくとも純粋な JavaScript のライブラリの思考は必ず使える
+  for (const b of ['montecarlo', 'range', 'madehand']) assert.ok(brains.includes(b), b);
+  for (const brain of brains) {
+    const rng = seeded(brain.length * 101);
+    let decisions = 0;
+    for (let game = 0; game < 6; game++) {
+      const n = 2 + (game % 5);
+      const stacks = Array.from({ length: n }, () => 100 + Math.floor(rng() * 1500));
+      const t = makeTable(stacks, { mode: 'friends' });
+      t.start(T(0), 0);
+      let now = 0;
+      for (let step = 0; step < 3000 && t.hand && t.hand.number <= 8; step++) {
+        const h = t.hand;
+        if (!h.finished && h.toAct != null) {
+          const style = ai.randomStyle(rng, brain);
+          assert.equal(style.brain, brain);
+          // 思考そのものがエラーにならず、何かを返す（バランス型に頼らない）
+          assert.ok(ai.BRAINS[brain].decide(h, h.toAct, { style, rng, iterations: 80 }), brain);
+          const d = ai.decide(h, h.toAct, { style, rng, iterations: 80 });
+          assert.equal(h.act(h.toAct, d.type, d.amount), null, `${brain} ${JSON.stringify(d)}`);
+          decisions++;
+        } else {
+          t.tick((now += 10 ** 5));
+        }
+      }
+    }
+    assert.ok(decisions > 60, `${brain} decisions=${decisions}`);
+  }
+});
+
+test('CPU: 思考の性格は弱い手で降り、強い手では降りない', () => {
+  for (const brain of ai.availableBrains()) {
+    const rng = seeded(3);
+    const t = makeTable([1000, 1000, 1000], { mode: 'friends' });
+    t.start(T(0), 0);
+    const h = t.hand;
+    const [sb, bb, btn] = h.order;
+    rig(h, [['7c', '2d'], ['8h', '3s'], ['As', 'Ah']], ['Kd', '9c', '4s', '5h', 'Jd']);
+    const style = ai.randomStyle(rng, brain);
+    assert.notEqual(ai.decide(h, btn, { style, rng }).type, 'fold', brain); // AA
+    t.act(tk(t, btn), 'raise', 1000); // オールイン
+    assert.equal(ai.decide(h, sb, { style, rng }).type, 'fold', brain); // 72o
+  }
+});
+
+test('CPU戦: CPU ごとに違う思考が割り当てられ、どれを使っているかは画面に出ない', () => {
+  const brains = ai.availableBrains();
+  assert.deepEqual(new Set(ai.makeStyles(brains.length).map((s) => s.brain)), new Set(brains));
+  const t = new Table({
+    id: 'c',
+    name: 'cpu',
+    startingStack: 1000,
+    smallBlind: 10,
+    bigBlind: 20,
+    blindTimerEnabled: false,
+    blindIntervalMin: 10,
+    hostToken: T(0),
+    mode: 'cpu',
+    cpuCount: 8,
+  });
+  const used = new Set(t.seats.filter((s) => s && s.bot).map((s) => s.style.brain));
+  assert.equal(used.size, brains.length);
+  t.join(T(0), 'me');
+  t.start(T(0), 0);
+  const json = JSON.stringify([t.publicState(T(0), new Set()), t.summary()]);
+  for (const word of ['brain', 'style', ...brains, 'aggression', 'Threshold']) assert.ok(!json.includes(word), word);
+});
+
 test('CPU戦: CPU が席に着き、ホストは人間のまま、CPU は自動で行動する', () => {
   const t = new Table({
     id: 'c',