Add a settings page for profit display and default stack

- Per-device toggle to hide your own net and the net ranking at tables
- Default starting stack set in settings; creating a table saves the
  stack, SB and BB used as the next defaults
- Number fields on create and settings select all on focus

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

public/lobby.html

@@ -38,6 +38,11 @@
           <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>
+        <a class="cell cell-link" href="/settings">
+          <span class="cell-icon tone-gray"><svg class="i" viewBox="0 0 24 24" aria-hidden="true"><path d="M4 7h9M17 7h3M4 17h3M11 17h9"/><circle cx="15" cy="7" r="2"/><circle cx="9" cy="17" r="2"/></svg></span>
+          <span class="cell-title">設定<span class="cell-sub">収支の表示・開始スタック</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>