[Roadmap] Add Makie.jl plotting backend

[ocots]

Objective

Add Makie.jl as a plotting backend alongside the existing Plots.jl support in CTModels.

Why

Makie.jl offers superior performance (GPU-accelerated), rich interactivity, and better support for complex visualizations. Providing it as an alternative backend gives users more flexibility. This is part of the broader plot engine work (CTModels #363).

References

• Plot engine discussion
• Makie.jl
• Roadmap comment