Honor URDF collision visualization option

[sylvesterkaczmarek]

Description

Make the USD-to-URDF exporter's visualize_collision_meshes option control whether collision geometry is also emitted as visual geometry.

The converter already exposes and stores this option, but it was not passed to link conversion. At the same time, default-purpose geometry with CollisionAPI was classified as both collision and visual, so disabling Visualize Collisions could still produce collision boxes under both <collision> and <visual>.

This change threads the option into read_link(). Collision geometry remains in <collision> in both modes; it is duplicated into <visual> only when visualize_collision_meshes=True.

Validation

• regression test covers the default disabled behavior
• regression test covers explicitly enabled collision visualization
• normal non-collision visual classification is unchanged

Addresses #709.