[omniperf-agent] fix: PhysX KukaAllegro grasp via compliant contacts

[yts-nv]

Under rigid PhysX contacts the manipulated object is squirted out of the dexterous KukaAllegro hand before a sustained thumb+finger pinch forms, so the good_finger_contact grasp reward stays 0 and PPO never learns to lift; the object leaves the workspace and episodes terminate early. Newton (soft-constraint contacts) converges on the same task.

Fix: give the object a PhysX compliant (soft) contact material so the fingers can hold it, and disable the startup material domain randomization that rebuilds/rebinds the object material at startup and would otherwise discard the compliant spawn material.

Validated on the upstream core/lift KukaAllegro layout:
success_rate 0 -> 0.40 @2000 iters, 0.78 @4000 (Newton-level),
reproduced 2x (env seed 42). Not re-trained on this dexsuite layout;
reviewer should validate before merge.

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