Faster startup

To remove most of the first-run compilation before a demo, build a custom sysimage once and launch TerraScope with it:

julia --project=. scripts/build_sysimage.jl
julia --project=. -J build/TerraScopeSysimage.dll examples/launch_TerraScope3D.jl

This does not eliminate file I/O, Windows display setup or GL context creation, but it substantially reduces Julia compilation and makes startup more consistent across runs.

Windows launcher

On Windows, run the launcher in the repository root:

Launch-TerraScope.cmd

It uses the sysimage automatically when it exists and offers to build it the first time.