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

src/rendering/character_renderer.cpp

@@ -21,6 +21,7 @@
 #include "rendering/vk_shader.hpp"
 #include "rendering/vk_buffer.hpp"
 #include "rendering/vk_utils.hpp"
+#include "rendering/vk_frame_data.hpp"
 #include "rendering/camera.hpp"
 #include "pipeline/asset_manager.hpp"
 #include "pipeline/blp_loader.hpp"
@@ -2678,8 +2679,6 @@ void CharacterRenderer::renderShadow(VkCommandBuffer cmd, const glm::mat4& light
     vkCmdBindDescriptorSets(cmd, VK_PIPELINE_BIND_POINT_GRAPHICS, shadowPipelineLayout_,
         1, 1, &shadowParamsSet_, 0, nullptr);
 
-    struct ShadowPush { glm::mat4 lightSpaceMatrix; glm::mat4 model; };
-
     const float shadowRadiusSq = shadowRadius * shadowRadius;
     for (auto& pair : instances) {
         auto& inst = pair.second;

src/rendering/m2_renderer.cpp

@@ -3070,7 +3070,6 @@ void M2Renderer::renderShadow(VkCommandBuffer cmd, const glm::mat4& lightSpaceMa
     if (!shadowPipeline_ || !shadowParamsSet_) return;
     if (instances.empty() || models.empty()) return;
 
-    struct ShadowPush { glm::mat4 lightSpaceMatrix; glm::mat4 model; };
     struct ShadowParamsUBO {
         int32_t useBones = 0;
         int32_t useTexture = 0;

src/rendering/terrain_renderer.cpp

@@ -965,7 +965,6 @@ void TerrainRenderer::renderShadow(VkCommandBuffer cmd, const glm::mat4& lightSp
 
     // Identity model matrix — terrain vertices are already in world space
     static const glm::mat4 identity(1.0f);
-    struct ShadowPush { glm::mat4 lightSpaceMatrix; glm::mat4 model; };
     ShadowPush push{ lightSpaceMatrix, identity };
     vkCmdPushConstants(cmd, shadowPipelineLayout_, VK_SHADER_STAGE_VERTEX_BIT,
                        0, 128, &push);

src/rendering/wmo_renderer.cpp

@@ -1715,8 +1715,6 @@ void WMORenderer::renderShadow(VkCommandBuffer cmd, const glm::mat4& lightSpaceM
     vkCmdBindDescriptorSets(cmd, VK_PIPELINE_BIND_POINT_GRAPHICS, shadowPipelineLayout_,
         0, 1, &shadowParamsSet_, 0, nullptr);
 
-    struct ShadowPush { glm::mat4 lightSpaceMatrix; glm::mat4 model; };
-
     // WMO shadow cull uses the ortho half-extent (shadow map coverage) rather than
     // the proximity radius so that distant buildings whose shadows reach the player
     // are still rendered into the shadow map.