feat: add /who results window with sortable player table

Store structured WhoEntry data from SMSG_WHO responses and show them
in a dedicated popup window with Name/Guild/Level/Class/Zone columns.
Right-click on any row to Whisper, Invite, Add Friend, or Ignore.
Window auto-opens when /who or /whois is typed; shows online count
in the title bar. Results persist until the next /who query.

include/ui/game_screen.hpp

@@ -396,6 +396,10 @@ private:
     int bagBarPickedSlot_ = -1;   // Visual drag in progress (-1 = none)
     int bagBarDragSource_ = -1;   // Mouse pressed on this slot, waiting for drag or click (-1 = none)
 
+    // Who Results window
+    bool  showWhoWindow_ = false;
+    void  renderWhoWindow(game::GameHandler& gameHandler);
+
     // Instance Lockouts window
     bool  showInstanceLockouts_ = false;