Isolate maple table background

[xyao-nv]

Summary

Before:
Arena/assets/object_library/srl_robolab_assets/scenes/maple_table_robolab.usda
(will be removed from OV once this MR is merged)

After:
maple table background: Arena/assets/object_library/srl_robolab_assets/scenes/maple_table.usda
robot stand added in droid.py: Arena/assets/object_library/srl_robolab_assets/robots/franka_stand_grey.usda

[greptile-apps]

Greptile Summary

This PR isolates the maple table background into a standalone USD asset and replaces the generic Isaac stand in droid.py with a purpose-built franka_stand_grey.usda from the Nucleus asset library.

• background_library.py: Updates MapleTableRobolab.usd_path from the old combined scene (maple_table_background.usda) to the new isolated background asset (maple_table.usda).
• droid.py: Swaps the robot stand from the remote S3-hosted stand_instanceable.usd to the internal Nucleus-hosted franka_stand_grey.usda, retaining the existing scale=(1.2, 1.2, 1.7) and activate_contact_sensors=False.

Confidence Score: 5/5

Both changes are asset path swaps with no logic modifications; safe to merge once the new USD files are confirmed present at their Nucleus paths.

The changes replace two USD asset paths — a straightforward refactor with no impact on simulation logic, physics settings, or configuration contracts. The main open questions (physics properties and scale fit for the new stand) were already raised in prior review comments and are non-blocking.

No files require special attention beyond verifying the new USD assets exist on Nucleus at the declared paths.

Important Files Changed

Filename	Overview
isaaclab_arena/assets/background_library.py	Simple one-line path rename from maple_table_background.usda to maple_table.usda; no logic changes.
isaaclab_arena/embodiments/droid/droid.py	Replaces the remote S3 generic stand with the internal Nucleus franka_stand_grey.usda; scale and other spawn settings are unchanged from the previous asset.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A[MapleTableRobolab] -->|usd_path| B["NUCLEUS/.../scenes/maple_table.usda\n(was: maple_table_background.usda)"]
    
    C[DroidSceneCfg.stand] -->|usd_path| D["NUCLEUS/.../robots/franka_stand_grey.usda\n(was: S3 Isaac stand_instanceable.usd)"]
    D --> E["scale=(1.2, 1.2, 1.7)\nactivate_contact_sensors=False"]

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_{Reviews (2): Last reviewed commit: "lint" | Re-trigger Greptile}

[cvolkcvolk]

Thanks!