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/Core/IEditorContext.h

@@ -0,0 +1,24 @@
+#pragma once
+
+#include <memory>
+#include <string>
+
+namespace XCEngine {
+namespace Editor {
+
+class EventBus;
+class ISelectionManager;
+
+class IEditorContext {
+public:
+    virtual ~IEditorContext() = default;
+    
+    virtual EventBus& GetEventBus() = 0;
+    virtual ISelectionManager& GetSelectionManager() = 0;
+    
+    virtual void SetProjectPath(const std::string& path) = 0;
+    virtual const std::string& GetProjectPath() const = 0;
+};
+
+}
+}