Robot descriptions v2.13.0

Robot and standalone gripper descriptions v2.13.0

Eight self-contained downloads, each including meshes, materials, collisions,
joints, frame definitions and physical properties:

Product	MuJoCo	URDF
PAR6, all six mounted tools	par6_mujoco.zip	par6_urdf.zip
PAROL6, all six mounted tools	parol6_mujoco.zip	parol6_urdf.zip
MSG only: Solid / Soft TPU jaws	msg_mujoco.zip	msg_urdf.zip
SSG48 only: Solid / Fin-ray jaws	ssg48_mujoco.zip	ssg48_urdf.zip

The new gripper-only exports reuse the maintained tool subtrees at the physical
flange frame. Local inertials, mass targets, joint origins/axes/limits,
coupling, collision surfaces and materials are preserved. MSG's camera is
included. A fixed native mounting frame supports standalone visualization;
there is no arm or grasp-test fixture in the gripper models.

The original PAR6/PAROL6 definitions and physical settings remain unchanged.
MSG retains its existing opposing-jaw contact before the mathematical joint
limit; physical close/open checks verify contact and reopening. Tool COM/inertia,
motor rotor inertia and some control parameters remain uncalibrated estimates.
Soft TPU and Fin-ray material deformation is not simulated.

Validation covers four standalone jaw profiles, both formats' FK and physical
properties, finite native close/open behavior, and all four relocated gripper
packages. Existing arm, collision and grasp regressions and the full independent
build remain part of release validation. ZIPs are extracted and checked without
referring back to the authoring repository. Checksums and the source commit are
recorded in SHA256SUMS and release_manifest.json.

For product-specific instructions, open description/ in the corresponding
hardware repository, or choose a guide from the shared repository's README.