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/assets/lobby.js

@@ -61,6 +61,7 @@
                 <span>開始 <b>${chips(t.startingStack)}</b></span>
                 <span class="gold">Lv.${t.level} <b class="gold">${chips(t.smallBlind)}/${chips(t.bigBlind)}</b></span>
                 <span>${timer}</span>
+                ${t.cardsEnabled ? '<span>🃏 カードあり</span>' : ''}
               </div>
             </div>
             <button class="btn btn-blue btn-sm" data-join="${esc(t.id)}" ${full ? 'title="満席（観戦のみ）"' : ''}>