Flat circular disc on XY centered at origin. Center vertex + ring
of <segments>+1 vertices (extra one to break the UV seam),
indexed as a fan.
Useful for magic circles, coin meshes, lily pads, top caps for
cylinders the user wants without making a full cylinder, table
tops, etc. UV mapping is centered (0.5, 0.5) at the disc's center
and unit-circle-aligned at the rim, so radial textures (like the
new --gen-texture-rings) align correctly.
Args: <wom-base> [radius] [segments]
Defaults: radius 1.0, segments 32. Hard-capped at 1024 segments.
Verified: radius 0.5 / segments 24 produces 26 verts / 24 tris.
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