fix(sac): adjust G1 WBT reset and push velocities

[mothinf]

Summary

• what changed
• why it changed
• any user-facing or training-impact behavior

Linked Work

• Issue:
• Parent roadmap (when applicable):
• Roadmap declared base (when applicable):
• Milestone:
• Base branch:

Validation

• make test-all passed on the final local head before this PR was created or updated
• Additional task-specific validation listed below

Commands actually run:

# paste exact commands here

Remote CI route:

• Base main: record the current-head CI link and status here.
• Any other base: write not scheduled; local make test-all is the test gate.

Impact

• Backend impact: mujoco / motrix / both / none
• Platform impact: macOS / Linux / both / unknown
• Training effect expected: yes / no / unknown

Artifacts

• W&B:
• benchmark result:
• video / screenshot:
• ONNX / checkpoint:

Checklist

• Added or updated tests where needed
• Updated docs if behavior or workflow changed
• Linked the driving issue
• Noted any follow-up work explicitly