Add an auto-paint preview toggle for simulated colors vs physical layer colors

Auto-paint could use a preview toggle in the 3D model preview area that switches between the estimated/simulated final colors and the actual physical layer or filament colors.

The goal is to help users understand both sides of the auto-paint result:

• what the print is expected to look like after color blending/transmission
• what colors/filaments are actually being stacked in the generated model

Suggested behavior:

• Add the toggle to the 3D preview controls, near view controls such as camera mode or future wireframe/transparent view modes.
• One view shows the estimated final appearance/colors.
• One view shows the real layer/filament colors used by the model.
• The toggle should affect preview/inspection only, not change the generated export.
• The current view mode should be clearly labeled so users know what they are looking at.
• The control should only appear, or only become active, when an auto-paint model/view supports both color interpretations.

Why this matters:
Auto-paint can produce colors through layered blending, so the visual result may not match the raw filament colors layer by layer. Being able to switch between these views would make the generated model easier to inspect, debug, and trust before printing.

Desired outcome:
Users can quickly compare the simulated auto-paint appearance against the actual physical colors used in the layer stack from the 3D preview itself, without changing print settings or export behavior.

Start in the 3D preview controls and the auto-paint model/view handling. Trace how the preview currently displays simulated colors and physical layer or filament colors, then identify where a labeled view toggle can be limited to supported auto-paint views. Done means users can switch between both appearances in the preview without changing generated exports or print settings.