Refactor vertical card stacking with opt-in overflow for variable zone sizes

Introduce a shared vertical stacking layout system in SelectZone that replaces the old divideCardSpaceInZone() free function with structured layout computation (StackLayoutParams, ZoneLayout, computeZoneLayout).

By default, cards are guaranteed to fit within zone bounds (no overflow). Zones can opt-in to bottom overflow via allowBottomOverflow flag, with sqrt-scaled compression for smooth visual transitions. A clip container mechanism is available for future zones that need visual clipping.

  Key changes:
  - SelectZone: new layout engine with allowBottomOverflow opt-in; clip container infrastructure for future zones needing visual clipping
  - StackZone: uses new layout (no overflow); adds setHeight() for dynamic resizing capabilities
  - HandZone: vertical layout delegates to SelectZone's shared stacking
  - AbstractCardItem: preserves hover z-value during layout passes; invalidates scene rect on hover exit for proper sibling repainting
  - CardZone::onCardAdded made virtual for clip container reparenting
  - Zone widths updated to CardDimensions::WIDTH_F * 1.5

cockatrice/src/game/zones/card_zone.cpp

@@ -19,6 +19,7 @@ CardZone::CardZone(CardZoneLogic *_logic, QGraphicsItem *parent)
 void CardZone::onCardAdded(CardItem *addedCard)
 {
     addedCard->setParentItem(this);
+    addedCard->setVisible(true);
     addedCard->update();
 }