7b1e76c791
Add configurable appearance mode system with two modes: - Realistic: material passthrough (restores original ShapeColor) - Engineering: colors parts by KindredCategory using Catppuccin Mocha palette KindredCategory enum property (custom_body, fastener, structural, electrical, seal_gasket, bearing_bushing, spring_compliant, moving_part) is added lazily to Part::Feature objects when Engineering mode is activated. Includes: - AppearanceMode base class with apply/reset/apply_to_object interface - AppearanceManager singleton with document observer for auto-coloring - Palette loaded from JSON config (theme-overridable) - View > Appearance Mode menu and toolbar integration - Preference persistence at Kindred/AppearanceMode Closes #20