feat(command-zone): add foundational type definitions

Add core type definitions and constants for the command zone feature:

- zone_names.h: Add command zone name constants (command, partner,
  companion, background) for protocol and lookup operations
- command_zone_types.h: Define CommandZoneType enum, ZoneVisibility enum,
  and StateChangeResult struct for state machine logic
- counter_ids.h: Define shared counter IDs and names for commander tax
  tracking (IDs 8-9 reserved to avoid conflicts with user counters)

These headers are intentionally minimal and dependency-free to enable
inclusion in both production code and isolated unit tests.

cockatrice/src/game/zones/command_zone_types.h

@@ -0,0 +1,87 @@
+/**
+ * @file command_zone_types.h
+ * @ingroup GameGraphicsZones
+ * @brief Type definitions for command zone state management.
+ *
+ * This header is intentionally minimal and dependency-free so it can be
+ * included in both production code and isolated unit tests.
+ */
+
+#ifndef COCKATRICE_COMMAND_ZONE_TYPES_H
+#define COCKATRICE_COMMAND_ZONE_TYPES_H
+
+/**
+ * @enum CommandZoneType
+ * @brief Identifies the type of command zone.
+ *
+ * Each zone type has different behavior:
+ * - Primary: Always visible, never collapsible, has tax counter
+ * - Partner: Collapsible, has tax counter
+ * - Companion: Collapsible, no tax counter
+ * - Background: Collapsible, no tax counter
+ */
+enum class CommandZoneType
+{
+    Primary,   ///< Main commander - always visible, never collapsible
+    Partner,   ///< Partner commander
+    Companion, ///< Companion
+    Background ///< Background
+};
+
+/**
+ * @enum ZoneVisibility
+ * @brief Represents the visual display state of a zone.
+ */
+enum class ZoneVisibility
+{
+    Expanded,  ///< Full height, cards visible
+    Minimized, ///< 25% height, cards clipped
+    Collapsed  ///< Zero height, only toggle button visible (not valid for Primary)
+};
+
+/**
+ * @namespace CommandZoneConstants
+ * @brief Constants for command zone sizing.
+ */
+namespace CommandZoneConstants
+{
+constexpr double MINIMIZED_HEIGHT_RATIO = 0.25;
+}
+
+/**
+ * @brief Returns whether the given zone type supports multiple cards.
+ *
+ * Primary and Partner zones hold exactly one card (commander rules,
+ * tax counter positioning). Companion and Background zones support
+ * multiple cards to handle rare mechanics like multiple companions.
+ *
+ * @param type The command zone type to check
+ * @return true if the zone can hold multiple cards, false for single-card zones
+ */
+inline bool supportsMultipleCards(CommandZoneType type)
+{
+    return type == CommandZoneType::Companion || type == CommandZoneType::Background;
+}
+
+/**
+ * @struct StateChangeResult
+ * @brief Result of a state mutation. Use the boolean flags to determine side effects;
+ * do not interpret visibility transitions directly (information hiding principle).
+ */
+struct StateChangeResult
+{
+    bool geometryChanged;     ///< Caller should call prepareGeometryChange() and update layout
+    bool shouldEmitExpanded;  ///< Caller should emit expandedChanged(isExpanded())
+    bool shouldEmitMinimized; ///< Caller should emit minimizedChanged(isMinimized())
+
+    /**
+     * @brief Returns a result indicating no changes occurred.
+     * @return StateChangeResult with all flags false
+     */
+    static StateChangeResult noChange()
+    {
+        return {false, false, false};
+    }
+};
+
+#endif // COCKATRICE_COMMAND_ZONE_TYPES_H

cockatrice/src/game/zones/zone_names.h

@@ -23,6 +23,10 @@ constexpr const char *HAND = "hand";
 constexpr const char *DECK = "deck";
 constexpr const char *SIDEBOARD = "sb";
 constexpr const char *STACK = "stack";
+constexpr const char *COMMAND = "command";
+constexpr const char *PARTNER = "partner";
+constexpr const char *COMPANION = "companion";
+constexpr const char *BACKGROUND = "background";
 } // namespace ZoneNames
 
 #endif // ZONE_NAMES_H