feat(lights, sirens): add universal color_off support for sirens, lights, and materials

[CanerKaraca23]

Summary

Extends the per-vehicle color_off material and JSON configuration capability across all siren lights, vehicle lights, and material types.

Key Changes

• Siren Lights color_off: Allows siren points and dummy definitions in vehicle JSON configs to specify custom color_off values (hex #RRGGBB or RGB array/object).
• Universal Off-State Color Resolution: Updates LightManager::GetMaterialColor (src/features/lights/manager.cpp) and Sirens (src/features/sirens.cpp) to resolve custom off-colors for sirens, taillights, brakelights, indicators, fog lights, spotlights, and strobes.
• Graceful Fallback: Preserves default unlit material color when no explicit color_off is configured.