Replace native confirm() with an in-site confirmation dialog

Add App.confirm() in common.js: a promise-based dialog styled like the
site's modals, with a title, multi-line message and custom button labels.
Destructive actions use a red OK button and focus Cancel by default;
Escape and backdrop clicks cancel, and Tab stays inside the dialog.

Use it for folding when a check is possible, leaving the table,
confirming showdown winners and deleting tables from the lobby. After the
dialog closes, re-check that the action is still valid (turn not passed,
pot not already awarded, table still listed) before sending it.

Also add a "poker-test" launch config that runs on port 4672 with the
example keys from .env.example, for local browser testing.

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

public/assets/common.js

@@ -52,6 +52,77 @@
     toastTimer = setTimeout(() => { el.hidden = true; }, 2500);
   }
 
+  // ブラウザ標準の confirm() の代わりの確認ダイアログ。OK なら true で解決する。
+  // opts: { title, message（改行可）, ok, cancel, danger（OK を赤にする） }
+  // 新しいダイアログを開くと、開いていたものはキャンセル扱いで閉じる
+  let closeConfirm = null;
+  function confirmDialog(opts) {
+    const o = typeof opts === 'string' ? { message: opts } : opts;
+    if (closeConfirm) closeConfirm(false);
+
+    const backdrop = document.createElement('div');
+    backdrop.className = 'modal-backdrop confirm-backdrop';
+    backdrop.innerHTML =
+      '<div class="modal confirm-modal" role="alertdialog" aria-modal="true">' +
+      (o.title ? '<h2 class="confirm-title"></h2>' : '') +
+      '<p class="confirm-message"></p>' +
+      '<div class="confirm-buttons">' +
+      '<button type="button" class="btn btn-dark" data-confirm="cancel"></button>' +
+      `<button type="button" class="btn ${o.danger ? 'btn-red' : 'btn-orange'}" data-confirm="ok"></button>` +
+      '</div></div>';
+    const dialog = backdrop.firstChild;
+    const msgEl = dialog.querySelector('.confirm-message');
+    msgEl.textContent = o.message || '';
+    msgEl.id = 'confirm-message-' + randomHex(4);
+    dialog.setAttribute('aria-describedby', msgEl.id);
+    if (o.title) {
+      const titleEl = dialog.querySelector('.confirm-title');
+      titleEl.textContent = o.title;
+      titleEl.id = 'confirm-title-' + randomHex(4);
+      dialog.setAttribute('aria-labelledby', titleEl.id);
+    }
+    const okBtn = dialog.querySelector('[data-confirm="ok"]');
+    const cancelBtn = dialog.querySelector('[data-confirm="cancel"]');
+    okBtn.textContent = o.ok || 'OK';
+    cancelBtn.textContent = o.cancel || 'キャンセル';
+
+    const prevFocus = document.activeElement;
+    return new Promise((resolve) => {
+      function close(result) {
+        if (closeConfirm !== close) return;
+        closeConfirm = null;
+        document.removeEventListener('keydown', onKey, true);
+        backdrop.remove();
+        if (prevFocus && prevFocus.focus && document.contains(prevFocus)) prevFocus.focus();
+        resolve(result);
+      }
+      function onKey(e) {
+        if (e.key === 'Escape') {
+          e.preventDefault();
+          close(false);
+        } else if (e.key === 'Tab') {
+          // フォーカスをダイアログの2つのボタンの中に閉じ込める
+          e.preventDefault();
+          (document.activeElement === okBtn ? cancelBtn : okBtn).focus();
+        }
+      }
+      okBtn.addEventListener('click', () => close(true));
+      cancelBtn.addEventListener('click', () => close(false));
+      // 背景を押したらキャンセル（ダイアログ内から背景へのドラッグは除く）
+      backdrop.addEventListener('pointerdown', (e) => {
+        backdrop.dataset.downOnBackdrop = e.target === backdrop ? '1' : '';
+      });
+      backdrop.addEventListener('click', (e) => {
+        if (e.target === backdrop && backdrop.dataset.downOnBackdrop) close(false);
+      });
+      document.addEventListener('keydown', onKey, true);
+      closeConfirm = close;
+      document.body.appendChild(backdrop);
+      // 危険な操作はうっかり Enter で確定しないようキャンセルにフォーカスする
+      (o.danger ? cancelBtn : okBtn).focus();
+    });
+  }
+
   async function api(method, url, body) {
     const res = await fetch(url, {
       method,
@@ -96,5 +167,5 @@
     FINISHING: 'FINISHING',
   };
 
-  window.App = { Store, esc, chips, toast, api, connectSocket, safeNext, PHASE_LABELS };
+  window.App = { Store, esc, chips, toast, confirm: confirmDialog, api, connectSocket, safeNext, PHASE_LABELS };
 })();