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>

public/lobby.html

@@ -33,6 +33,11 @@
           <label for="name">名前</label>
           <input id="name" type="text" maxlength="12" placeholder="例: とらのすけ" autocomplete="nickname">
         </div>
+        <a class="cell cell-link" href="/stats">
+          <span class="cell-icon tone-blue"><svg class="i" viewBox="0 0 24 24" aria-hidden="true"><path d="M12 3.5l8 8.5-8 8.5-8-8.5z"/><path d="M12 8l4 4-4 4-4-4z"/></svg></span>
+          <span class="cell-title">統計<span class="cell-sub">プレイスタイル・VPIP・PFR など</span></span>
+          <svg class="i chevron" viewBox="0 0 24 24" aria-hidden="true"><path d="M9 5l7 7-7 7"/></svg>
+        </a>
       </div>
       <div class="error-text" id="name-error" role="alert"></div>
     </section>