Map of scenes by name.
The shared ticker driving updates.
Logical viewport width.
Logical viewport height.
Center X of the viewport (width / 2).
Center Y of the viewport (height / 2).
Current time in milliseconds (from ticker).
Starts the ticker loop (begins emitting "tick" events).
Stops the ticker loop.
Top-level game manager that owns scenes and a shared ticker.
Coordinates updates across all scenes and provides viewport utilities.