Fix editor selection system: SelectionManager ID types and Scene lookup

- SelectionManager now implements ISelectionManager interface with uint64_t IDs
- Remove SelectionManager/SceneManager circular dependency via EventBus
- Add Scene::FindByID() for proper ID-based entity lookup
- SceneManager::GetEntity() now uses FindByID instead of name-based Find
- Fix editor CMakeLists.txt XCEngine.lib path
- EventBus now thread-safe with shared_mutex

editor/src/panels/Panel.h

@@ -1,6 +1,8 @@
 #pragma once
 
 #include <string>
+#include <memory>
+#include <cassert>
 
 namespace XCEngine {
 namespace Editor {
@@ -23,8 +25,16 @@ public:
     void SetOpen(bool open) { m_isOpen = open; }
     void Toggle() { m_isOpen = !m_isOpen; }
 
-    void SetContext(IEditorContext* context) { m_context = context; }
-    IEditorContext* GetContext() const { return m_context; }
+    void SetContext(IEditorContext* context) { 
+        assert(!m_context && "Context already set!");
+        m_context = context; 
+    }
+    
+    IEditorContext* GetContext() const { 
+        return m_context; 
+    }
+
+    bool HasContext() const { return m_context != nullptr; }
 
 protected:
     std::string m_name;