Reorganize directory layout: editor panels/, grouped shaders, drop stale header

- App/editor: move 7 panels into panels/ (Editor core stays at root)
- shaders/: group into pbr/ post/ debug/ env/ (runtime load paths updated)
- Delete outdated duplicate Engine/src/Renderer/VulkanAssetUploader.h

shaders/env/shadow.frag

@@ -0,0 +1,7 @@
+#version 450
+
+// Shadow pass fragment：depth-only，无输出。
+// 深度写入由深度附件 + 光栅化完成（含管线深度 bias）。
+
+void main() {
+}