MuJoCo-ready FluxWeave URDF package

Use after unzipping this package:

python - <<'PY'
import mujoco
model = mujoco.MjModel.from_xml_path("urdf/RSReBot_fluxweave_dm_mujoco.urdf")
print(model.nbody, model.njnt, model.ngeom)
PY

Notes:
- URDF mesh paths are written as ../meshes/*.stl relative to the urdf/ folder.
- STL files are exported as binary STL for MuJoCo compatibility.
- This package contains geometry and joints. Add actuators/inertials separately if you need closed-loop control.
