Refactor camera control logic in `MainController` to use the State design pattern.
- Create a new `core/camera/states.py` module with state classes (`NoCamerasState`, `DetectingState`, `ReadyToStreamState`, `StreamingState`).
- `MainController` now acts as a context, delegating actions to the current state object.
- This replaces complex conditional logic with a robust, scalable, and maintainable state machine, making it easier to manage camera behavior and add new states in the future.
