Refactor event handling and controller initialization for improved clarity

- Moved event handling logic from the Controller class to a new HandleEvents function in the Window class, enhancing separation of concerns.
- Simplified the OnEntry method by removing the Initialize function call and directly initializing the editor manager.
- Updated the OnLoad method to check for window activity, improving the logic for managing the controller's active state.
- Cleaned up the controller header by removing the obsolete Initialize method, streamlining the interface.

src/app/core/controller.h

@@ -24,7 +24,6 @@ class Controller {
  public:
   bool IsActive() const { return active_; }
   absl::Status OnEntry(std::string filename = "");
-  void Initialize(std::string filename = "");
   void OnInput();
   absl::Status OnLoad();
   void DoRender() const;