Added habitat level controls — build up and down to grow or shrink habitat towers, plus demolish controls to tear levels back down. Landing pads are now toggleable so you can enable or disable them. Both are controlled through the HUD when the building is selected.

Made the asteroid field circular instead of the previous rectangular distribution, which looks much more natural. Added a toggleable FPS counter widget and a pointer debug pane for tuning glow settings on selected entities. Fixed the selection glow animation and click feedback. Added a ships debug toggle to the debug panel.