feat: show zone name on loading screen during world transitions

Add setZoneName() to LoadingScreen and display the map name from Map.dbc
as large gold text with drop shadow above the progress bar. Shown in both
render() and renderOverlay() paths. Zone name is resolved from gameHandler's
getMapName(mapId) during world load. Improves feedback during zone transitions.

include/rendering/loading_screen.hpp

@@ -30,6 +30,7 @@ public:
 
     void setProgress(float progress) { loadProgress = progress; }
     void setStatus(const std::string& status) { statusText = status; }
+    void setZoneName(const std::string& name) { zoneName = name; }
 
     // Must be set before initialize() for Vulkan texture upload
     void setVkContext(VkContext* ctx) { vkCtx = ctx; }
@@ -53,6 +54,7 @@ private:
 
     float loadProgress = 0.0f;
     std::string statusText = "Loading...";
+    std::string zoneName;
 
     int imageWidth = 0;
     int imageHeight = 0;