Refactor/z value constants (#6651)

* feat(z-values): add centralized Z-value constants infrastructure

Magic numbers scattered across the codebase make Z-value layering
hard to understand and maintain. Centralizing them provides:
- Self-documenting layer hierarchy
- Validation utilities for development
- Single source of truth for Z-value ranges

Two-tier header design:
- z_value_layer_manager.h: Foundation with constants and validation
- z_values.h: User-facing namespace with semantic constants

* refactor(z-values): replace magic Z-value numbers with ZValues constants

Magic numbers like 2000000007 are impossible to understand without
context. Named constants (ZValues::DRAG_ITEM) are self-documenting.

This intentionally renumbers overlay Z-values to use a cleaner offset
sequence. The relative stacking order is preserved, which is what
matters for correct rendering.

Each consumer now includes z_values.h and uses semantic constants
instead of magic numbers.

* refactor(z-values): removed redundant inline with contexpr, Updated doc, magic numbers removed from TableZone.

cockatrice/src/game/board/arrow_item.cpp

@@ -5,6 +5,7 @@
 #include "../player/player.h"
 #include "../player/player_actions.h"
 #include "../player/player_target.h"
+#include "../z_values.h"
 #include "../zones/card_zone.h"
 #include "card_item.h"
 
@@ -23,7 +24,7 @@ ArrowItem::ArrowItem(Player *_player, int _id, ArrowTarget *_startItem, ArrowTar
     : QGraphicsItem(), player(_player), id(_id), startItem(_startItem), targetItem(_targetItem), targetLocked(false),
       color(_color), fullColor(true)
 {
-    setZValue(2000000005);
+    setZValue(ZValues::ARROWS);
 
     if (startItem)
         startItem->addArrowFrom(this);