feat(command-zone): add logic layer with tests

Implement CommandZoneLogic - the card data management layer for zones.
This layer handles card insertion, removal, and ordering independently
of Qt graphics rendering.

Key components:
- CommandZoneLogic: manages card data within a zone
- AddCardAlgorithm: generic insertion algorithm for ordered zones
- CardZoneLogic modifications: integrate with existing zone hierarchy

Design decisions:
- Separation of data logic from graphics enables unit testing
- addCardImpl uses a stable insertion algorithm for consistent ordering
- Mock card items enable testing without Qt graphics dependencies

Test coverage verifies card insertion behavior across edge cases.

tests/command_zone/mocks/mock_card_item.h

@@ -0,0 +1,72 @@
+/**
+ * @file mock_card_item.h
+ * @brief Lightweight CardItem stub for command zone unit tests.
+ *
+ * This mock provides minimal CardItem functionality needed to test
+ * CommandZoneLogic::addCardImpl without pulling in graphics dependencies.
+ */
+
+#ifndef MOCK_CARD_ITEM_H
+#define MOCK_CARD_ITEM_H
+
+#include <QObject>
+#include <QString>
+
+/**
+ * @brief Stub CardRef for tests (avoids network/protobuf dependencies)
+ */
+struct CardRef
+{
+    QString name;
+    QString setCode;
+};
+
+/**
+ * @brief Lightweight CardItem mock for testing zone logic.
+ *
+ * Tracks method calls and state changes for verification in tests.
+ */
+class MockCardItem : public QObject
+{
+    Q_OBJECT
+public:
+    explicit MockCardItem(int _id = 1, QObject *parent = nullptr) : QObject(parent), id(_id)
+    {
+    }
+
+    // State tracking
+    int id;
+    bool visible = false;
+    bool resetStateCalled = false;
+    bool resetStateShowFaceDown = false;
+    CardRef cardRef;
+
+    // CardItem interface methods used by CommandZoneLogic::addCardImpl
+    [[nodiscard]] int getId() const
+    {
+        return id;
+    }
+    void setId(int _id)
+    {
+        id = _id;
+    }
+    void setVisible(bool v)
+    {
+        visible = v;
+    }
+    [[nodiscard]] bool isVisible() const
+    {
+        return visible;
+    }
+    void resetState(bool showFaceDown)
+    {
+        resetStateCalled = true;
+        resetStateShowFaceDown = showFaceDown;
+    }
+    void setCardRef(const CardRef &ref)
+    {
+        cardRef = ref;
+    }
+};
+
+#endif // MOCK_CARD_ITEM_H