access: move SelectedTrackerTargetCategory to anonymous namespace

The variable is only used within tracker.cpp, so remove the unnecessary
extern declaration from the header and place it in the anonymous
namespace alongside the other file-local tracker state.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Source/controls/tracker.cpp

@@ -50,10 +50,10 @@
 
 namespace devilution {
 
-TrackerTargetCategory SelectedTrackerTargetCategory = TrackerTargetCategory::Items;
-
 namespace {
 
+TrackerTargetCategory SelectedTrackerTargetCategory = TrackerTargetCategory::Items;
+
 TrackerTargetCategory AutoWalkTrackerTargetCategory = TrackerTargetCategory::Items; ///< Category of the active auto-walk target.
 int AutoWalkTrackerTargetId = -1;                                                   ///< ID of the target being auto-walked to, or -1 if inactive.
 

Source/controls/tracker.hpp

@@ -20,8 +20,6 @@ enum class TrackerTargetCategory : uint8_t {
 	DeadBodies,
 };
 
-extern TrackerTargetCategory SelectedTrackerTargetCategory;
-
 void CycleTrackerTargetKeyPressed();
 void NavigateToTrackerTargetKeyPressed();
 void AutoWalkToTrackerTargetKeyPressed();