Add Tier 8 commands: advanced targeting system

Targeting Commands:
- /cleartarget - Clear current target selection
- /targetenemy - Cycle to next hostile target (Tab equivalent)
- /targetfriend - Cycle to next friendly player
- /targetlasttarget, /targetlast - Switch to previous target
- /targetlastenemy - Cycle to previous hostile target
- /targetlastfriend - Cycle to previous friendly player
- /focus - Set current target as focus (client-side)
- /clearfocus - Clear focus target

Implementation:
- Added focusGuid and lastTargetGuid to GameHandler for client-side tracking
- setTarget() now automatically saves previous target to lastTargetGuid
- setFocus() and clearFocus() manage focus target with user feedback
- targetLastTarget() swaps current and previous targets
- targetEnemy() cycles through hostile entities (Units)
- targetFriend() cycles through friendly entities (Players)
- Both targetEnemy/targetFriend support reverse parameter for backwards cycling

Features:
- Focus targeting is client-side (no server opcode in 3.3.5a)
- Last target tracking happens automatically on every target change
- Enemy/friend cycling iterates through visible entities
- Provides user feedback when no targets available
- Tab-like cycling behavior with wraparound

All commands work entirely client-side for responsive targeting.

include/game/game_handler.hpp

@@ -202,6 +202,18 @@ public:
     bool hasTarget() const { return targetGuid != 0; }
     void tabTarget(float playerX, float playerY, float playerZ);
 
+    // Focus targeting
+    void setFocus(uint64_t guid);
+    void clearFocus();
+    uint64_t getFocusGuid() const { return focusGuid; }
+    std::shared_ptr<Entity> getFocus() const;
+    bool hasFocus() const { return focusGuid != 0; }
+
+    // Advanced targeting
+    void targetLastTarget();
+    void targetEnemy(bool reverse = false);
+    void targetFriend(bool reverse = false);
+
     // Inspection
     void inspectTarget();
 
@@ -646,6 +658,8 @@ private:
 
     // Targeting
     uint64_t targetGuid = 0;
+    uint64_t focusGuid = 0;              // Focus target
+    uint64_t lastTargetGuid = 0;         // Previous target
     std::vector<uint64_t> tabCycleList;
     int tabCycleIndex = -1;
     bool tabCycleStale = true;