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/assets/settings.js

@@ -0,0 +1,34 @@
+// 設定: この端末だけに保存する（localStorage）
+(function () {
+  'use strict';
+
+  const { Store, selectOnFocus } = App;
+  const $ = (id) => document.getElementById(id);
+
+  Fluid.navBar($('nav'), $('large-title'));
+
+  const showNet = $('show-net');
+  showNet.checked = Store.showNet;
+  showNet.addEventListener('change', () => {
+    Store.showNet = showNet.checked;
+    Fluid.haptic(6);
+  });
+
+  const stack = $('default-stack');
+  stack.value = Store.defaultStack;
+  selectOnFocus(stack);
+  // 正しい値のときだけ保存する。外したときに不正なら保存済みの値に戻す
+  stack.addEventListener('input', () => {
+    const n = Number(stack.value);
+    const ok = Number.isInteger(n) && n >= 10 && n <= 100000000;
+    stack.classList.toggle('invalid', stack.value !== '' && !ok);
+    if (ok) Store.defaultStack = n;
+  });
+  stack.addEventListener('blur', () => {
+    stack.classList.remove('invalid');
+    stack.value = Store.defaultStack;
+  });
+  stack.addEventListener('keydown', (e) => {
+    if (e.key === 'Enter') stack.blur();
+  });
+})();