refactor: consolidate duplicate ShadowPush structure definition

Move ShadowPush from 4 separate rendering modules (character_renderer,
m2_renderer, terrain_renderer, wmo_renderer) into shared vk_frame_data.hpp
header. This eliminates 4 identical local struct definitions and ensures
consistency across all shadow rendering passes. Add vk_frame_data.hpp include
to character_renderer.cpp.

include/rendering/vk_frame_data.hpp

@@ -25,5 +25,11 @@ struct GPUPushConstants {
     glm::mat4 model;
 };
 
+// Push constants for shadow rendering passes
+struct ShadowPush {
+    glm::mat4 lightSpaceMatrix;
+    glm::mat4 model;
+};
+
 } // namespace rendering
 } // namespace wowee