Simplify default scene lighting

[yuecideng]

Description

This PR simplifies default simulation lighting and updates the modular Gym tutorial for more predictable, finite runs.

The default scene now uses a lower-intensity environment emission light without an additional directional light. The tutorial no longer configures or randomizes a point light, randomizes table materials less frequently, and exits after five episodes.

Dependencies: None.

Type of change

• Bug fix (non-breaking change which fixes an issue)
• Enhancement (non-breaking change which improves an existing functionality)
• New feature (non-breaking change which adds functionality)
• Breaking change (existing functionality will not work without user modification)
• Documentation update

Screenshots

Not applicable.

Checklist

• I have run the black . command to format the code base.
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• Dependencies have been updated, if applicable.

[Copilot]

Pull request overview

This PR simplifies EmbodiChain’s default simulation lighting by relying solely on lower-intensity environment emission light (removing the default directional “sun” light), and updates the modular Gym tutorial to run predictably with finite episodes and reduced material randomization frequency.

Changes:

• Reduced default global lighting to environment emission only (no default directional light).
• Updated the modular Gym tutorial to remove point-light configuration/randomization and randomize table materials less frequently.
• Made the tutorial exit after 5 episodes instead of running indefinitely.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
scripts/tutorials/gym/modular_env.py	Removes point-light setup/randomization, reduces table material randomization frequency, and makes the tutorial loop finite.
embodichain/lab/sim/sim_manager.py	Simplifies default global lighting by removing the directional light and lowering emission intensity.

Comments suppressed due to low confidence (1)

scripts/tutorials/gym/modular_env.py:209

• The inner loop reuses the same loop variable name as the outer episode loop (i), shadowing it and making it easy to misread/debug the tutorial output. Use distinct names (e.g., episode_idx/step_idx) or _ if unused.

    for i in range(5):
        obs, info = env.reset()

        for i in range(100):
            action = torch.zeros(env.action_space.shape, dtype=torch.float32)

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