refactor(editor): Phase 1 architecture refactoring

- Decouple Panel from Core::Layer (P0 issue resolved)
- Add EventBus with type-safe event system
- Add ISelectionManager interface with SelectionManagerImpl
- Add IEditorContext for dependency injection
- Update EditorLayer to use new architecture
- Update Application to create and inject EditorContext

New files:
- editor/src/Core/EventBus.h
- editor/src/Core/EditorEvents.h
- editor/src/Core/ISelectionManager.h
- editor/src/Core/SelectionManagerImpl.h
- editor/src/Core/IEditorContext.h
- editor/src/Core/EditorContextImpl.h

This enables future improvements: Undo/Redo, serialization, component extensibility.

editor/src/Application.cpp

@@ -1,5 +1,6 @@
 #include "Application.h"
 #include "Layers/EditorLayer.h"
+#include "Core/EditorContextImpl.h"
 #include <XCEngine/Debug/Logger.h>
 #include <XCEngine/Debug/FileLogSink.h>
 #include <XCEngine/Debug/ConsoleLogSink.h>
@@ -115,8 +116,11 @@ bool Application::Initialize(HWND hwnd) {
         m_srvHeap->GetCPUDescriptorHandleForHeapStart(),
         m_srvHeap->GetGPUDescriptorHandleForHeapStart());
     
+    m_editorContext = std::make_shared<EditorContextImpl>();
+    m_editorContext->SetProjectPath(exeDir);
+    
     m_editorLayer = new EditorLayer();
-    m_editorLayer->SetProjectPath(exeDir);
+    m_editorLayer->SetContext(m_editorContext);
     m_layerStack.pushLayer(std::unique_ptr<Core::Layer>(m_editorLayer));
     m_layerStack.onAttach();