Add six-vessel grasp, lift, and placement environment

[Steafy7]

Scope

Adds the reusable six-vessel MatteriX environment and its registered task/workflow.

Included:

• environment/task configuration and registration;
• per-asset environment profile data;
• motion-primitive settling support used by the environment;
• workflow launcher support for livestreaming, episode limits, and recording paths.

Asset USD payloads are provided separately in the MatteriX_assets pull request.

This environment PR contains no asset payloads, qualification harnesses, logs, results, reports, runbooks, or workbench records.

The baseline renderer configuration is retained; no global translucency override is introduced here.

[Steafy7]

Superseded by consolidated testing-environment PR #9.