Add rigid-object gizmo window control

[yuecideng]

Description

This PR adds a default viewer interaction for manipulating raycast-selected rigid objects with a gizmo. Left-clicking an eligible rigid object and pressing G enables gizmo control; pressing G again exits.

Dynamic objects are temporarily switched to kinematic while controlled and restored to their original body type on disable, window close, or simulation teardown. The change also removes destroyed gizmos from the DexSim arena so they no longer remain visible after disable.

The hotkey is enabled by default and can be configured through SimulationManagerCfg.window_gizmo.enable_hotkey. Static objects and multi-environment simulations are rejected safely.

Dependencies: None.

Issue: Not linked.

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 included. The behavior is covered by automated lifecycle and cleanup tests.

Validation

• black .
• pytest -q tests/sim/objects/test_gizmo.py tests/sim/test_sim_manager.py — 13 passed
• pytest -q tests/ — 633 passed, 99 skipped
• make -C docs html — completed successfully with existing repository warnings

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. No dependency changes were required.

[yuecideng]

Close, this feature will be implemented in dexsim