How to Convert Input Manager to Input System (Unity 6.3 LTS)

Unity 6.3 LTS marks the Input Manager as deprecated in favor of the Input System package. The migration is straightforward with direct equivalents: `Input.GetKey()` becomes `Keyboard.current[key].isPressed`, `Input.mousePosition` becomes `Mouse.current.position.value`, and mouse buttons use `Mouse.current.rightButton.wasPressedThisFrame`. Mouse events like `OnMouseEnter()` require implementing interfaces like `IPointerEnter` and adding a Physics Raycaster component to the camera plus an Event System. The new Input System now offers simple shorthands for prototyping while maintaining powerful input action capabilities for production.