Add lab desk objects: lamp, laptop, plant, alligator, test tubes, medicine bottles

Replace blocks with realistic lab environment objects built from MuJoCo
primitives. Includes a desk lamp, laptop with dark IDE screen texture
and keyboard checker texture, fake plant, alligator trophy statue on
shelf, test tube rack with 6 manipulable colored tubes, and 4
manipulable medicine bottles. Repositions the original test tube stand
behind the new rack.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: davetcoleman