Add optional card mode: server deals cards and settles showdowns automatically

- New "カードを配る" switch on the create-table screen (default off); the lobby
  shows "カードあり" for tables that use it
- Card mode (server/cards.js restored): crypto-shuffled deck kept server-side,
  hole cards sent only to their owner until showdown/all-in reveal, board dealt
  per street with burns, all-in runout on a timer (frozen while paused)
- Showdown is evaluated and every pot (incl. side pots, split pots) is paid out
  automatically; host winner selection is only used when card mode is off
- Play UI: board, hole cards, own cards in the action bar, hand names, winning
  cards highlighted; layout tuned for 7+ seats and short screens
- Playing-card styles use .pcard so they don't clash with the existing .card panel
- Tests for hand evaluation, card privacy, runout, side pots, ties and random play

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

server/index.js

@@ -114,6 +114,7 @@ app.post('/api/tables', (req, res) => {
   const bigBlind = b.bigBlind;
   const blindTimerEnabled = b.blindTimerEnabled === true;
   const blindIntervalMin = b.blindIntervalMin;
+  const cardsEnabled = b.cardsEnabled === true;
   const hostToken = cleanToken(b.token);
 
   if (tables.tables.size >= config.MAX_TABLES) return res.status(429).json({ error: 'テーブル数が上限に達しています' });
@@ -132,6 +133,7 @@ app.post('/api/tables', (req, res) => {
     bigBlind,
     blindTimerEnabled,
     blindIntervalMin: blindTimerEnabled ? blindIntervalMin : 10,
+    cardsEnabled,
     hostToken,
   });
   broadcastLobby();
@@ -276,7 +278,7 @@ io.on('connection', (socket) => {
   });
 });
 
-// ブラインドタイマー・持ち時間・次のハンドなど時間で進む処理
+// ブラインドタイマー・オールイン後の場札・次のハンドなど時間で進む処理
 setInterval(() => {
   const now = Date.now();
   for (const table of tables.tables.values()) {