Use @pokertools/engine and evaluator for poker rules and hand ranking

Replace the hand-rolled betting rules, side pots, showdown and hand
evaluator with the published @pokertools/engine and @pokertools/evaluator
libraries (MIT, pinned to 2.1.0).

- server/hand.js now wraps a PokerEngine per hand: it maps seats,
  mirrors stacks, staggers the all-in runout, and pays host-chosen
  winners on cash-only tables.
- server/cards.js and server/ai.js use the library evaluator.
- Out-of-turn folds go through the engine's stand; all-in hands stay
  live when the player leaves; uncalled bets return to a leaver.
- The engine refuses some check-able folds that would leave a side pot
  without eligible players; those now return a message (or check for
  a leaving player) instead of crashing.
- BB must be greater than SB (engine requirement); Node >= 24.
- Tests rig cards via engine snapshots and cover the new edge cases.

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

public/assets/create.js

@@ -60,7 +60,7 @@
     const bb = int(bbInput);
     const on = timerInput.checked;
     intervalInput.disabled = !on;
-    scheduleEl.hidden = !on || !(sb > 0 && bb >= sb);
+    scheduleEl.hidden = !on || !(sb > 0 && bb > sb);
     if (scheduleEl.hidden) return;
     const mins = int(intervalInput) > 0 ? int(intervalInput) : 0;
     scheduleEl.innerHTML = Blinds.schedule(sb, bb, 8)
@@ -119,7 +119,7 @@
     if (!name) return [nameInput, 'テーブル名を入力してください'];
     if (!(stack >= 10)) return [stackInput, '開始スタックは10以上の整数にしてください'];
     if (!(sb >= 1)) return [sbInput, 'SBは1以上の整数にしてください'];
-    if (!(bb >= sb)) return [bbInput, 'BBはSB以上にしてください'];
+    if (!(bb > sb)) return [bbInput, 'BBはSBより大きくしてください'];
     if (bb > stack) return [bbInput, 'BBが開始スタックより大きいです'];
     if (timerInput.checked && !(interval >= 1 && interval <= 240)) return [intervalInput, 'インターバルは1〜240分にしてください'];
     return null;