Add player stats, in-table ranking, host seating and review return

- Stats page (/stats): play style radar (TAG/LAG/rock/fish), VPIP, PFR,
  ATS, 3bet, WTSD, W$SD, WWSF, per-street fold rate, aggression
  frequency, hand win rate and net in BB, per table type, each with a
  bands-and-explanation sheet. Hands are counted per human player when
  they finish and stored as totals under data/stats/, keyed by a hash
  of the player ID (sent in a POST body, never in the URL).
- Ranking sheet at the table: everyone seated, ordered by stack or by
  net (stack minus buy-ins), updating live.
- The host can reorder seats by dragging (with a mini table preview and
  shuffle). Takes effect immediately between hands, otherwise at the
  start of the next hand; the dealer button stays with the same player.
- The full-session review opens in the same tab and its back button
  returns to the table it was opened from.

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

test/engine.test.js

@@ -1,7 +1,11 @@
 'use strict';
 
-// node --test で実行（ACCESS_KEY はテスト用のダミー）
+// node --test で実行（ACCESS_KEY はテスト用のダミー、統計の保存先は一時ディレクトリ）
+const fs = require('fs');
+const os = require('os');
+const path = require('path');
 process.env.ACCESS_KEY = process.env.ACCESS_KEY || '000000';
+process.env.STATS_DIR = fs.mkdtempSync(path.join(os.tmpdir(), 'holdem-stats-'));
 
 const test = require('node:test');
 const assert = require('node:assert/strict');