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>

public/create.html

@@ -49,6 +49,15 @@
       </div>
       <div class="schedule" id="schedule" hidden></div>
 
+      <div class="switch-row">
+        <span>カードを配る</span>
+        <label class="switch">
+          <input id="cards" type="checkbox" aria-label="カードを配る">
+          <span></span>
+        </label>
+      </div>
+      <div class="hint" id="cards-hint">オフ: 実物のカードで遊び、ショーダウンの勝者はホストが選ぶ</div>
+
       <div class="error-text" id="error"></div>
       <button class="btn btn-orange btn-block mt-8" id="submit" type="submit">テーブルを作成</button>
     </form>