AnimationExport fails with push! MethodError on JSON.jl v1.x #144

Exporting an animation to three.js JSON (Scene(..., animationFile="...")) fails with current JSON.jl v1.x (tested v1.7.1), despite Project.toml allows JSON = "1".

Error:
ERROR: MethodError: no method matching push!(::JSON.Object{String, Any}, ::Pair{String, String}, ::Pair{String, String})
exportObject(...) @ Modia3D.AnimationExport src/AnimationExport/exportAnimation.jl:274

Root cause:
exportAnimation.jl parses mesh companion .json files via JSON.parse(io), then mutates the result with push!(dict, "key" => value, ...). This worked with JSON.jl v0.21, where JSON.parse returned a plain Dict{String,Any}. In JSON.jl v1.x, JSON.parse returns a custom JSON.Object{K,V} <: AbstractDict (linked-list based) that implements setindex!/delete! but not push!, so these calls fail.
Affected lines are in exportAnimation.jl.

Fix:
Replace push!(dict, "key" => value) with dict["key"] = value (setindex! instead of push!), which works for both Dict and JSON.Object. I verified against JSON.jl v1.7.1 by running test/ForceElements/PCMBouncingBubbles.jl with animationFile enabled — the simulation completes and produces a valid three.js JSON animation file. I attached the modified exportAnimation.jl file (as txt, since jl is not accepted as a source code file (funny, hah))
exportAnimation

Note: the existing test suite doesn't catch this since animationFile export is commented out in the shipped PCM test files.