refactor: extract CARD_HEIGHT to shared CardDimensions header (#6668)

* refactor: extract CARD_HEIGHT to shared CardDimensions header

  Move duplicated CARD_WIDTH/CARD_HEIGHT constants to card_dimensions.h.
  Fixed documentation in z_value_layer_manager.h.

* WIDTH_F used directly instead of casting

* Improved consistency and added missing newlines at end of files

cockatrice/src/game/card_dimensions.h

@@ -0,0 +1,29 @@
+#ifndef CARD_DIMENSIONS_H
+#define CARD_DIMENSIONS_H
+
+#include <QtGlobal>
+
+/**
+ * @file card_dimensions.h
+ * @brief Canonical card dimension constants for layout and Z-value calculations.
+ *
+ * These values represent the logical pixel dimensions of a standard card graphic.
+ * They are used throughout the game scene for layout, rendering, and Z-value computation.
+ */
+namespace CardDimensions
+{
+/// Card width in pixels
+constexpr int WIDTH = 72;
+/// Card height in pixels
+constexpr int HEIGHT = 102;
+
+/// Pre-converted for floating-point contexts (Z-value calculations)
+constexpr qreal WIDTH_F = static_cast<qreal>(WIDTH);
+constexpr qreal HEIGHT_F = static_cast<qreal>(HEIGHT);
+
+/// Half-dimensions for centering and rotation transforms
+constexpr qreal WIDTH_HALF_F = WIDTH_F / 2;
+constexpr qreal HEIGHT_HALF_F = HEIGHT_F / 2;
+} // namespace CardDimensions
+
+#endif // CARD_DIMENSIONS_H