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>

server/hand.js

@@ -56,6 +56,8 @@ class Hand {
     this.log = [];
     this.startStacks = new Map(order.map((s) => [s, seats[s].stack])); // ブラインドを払う前
     this.allIn = null; // オールインで決着した時点の場札とポット（レビューの期待値用）
+    this.startedAt = Date.now(); // 統計のプレイ時間用
+    this.endedAt = null;
 
     this.players = new Map();
     for (const i of order) {
@@ -413,7 +415,8 @@ class Hand {
   }
 
   end(showdown, results) {
-    this.endStacks = new Map(this.order.map((s) => [s, this.seats[s] ? this.seats[s].stack : 0])); // レビュー用
+    this.endStacks = new Map(this.order.map((s) => [s, this.seats[s] ? this.seats[s].stack : 0])); // レビュー・統計用
+    this.endedAt = Date.now();
     this.finished = true;
     this.runout = false;
     this.showdown = showdown;