v2.1.0 - Stable Full-Body Training

What's Changed

Training Stability Fixes

• Upright default pose: Replaced squat stance (knee 0.669 rad) with natural upright position (knee 0.3 rad)
• Balanced PD gains: waist_kp=100 (was 200→vibrations, 60→ragdoll)
• Higher spawn: 0.82m to accommodate straight legs
• New rewards: similar_to_default and track_pitch for posture guidance
• Curriculum: Reduced velocity commands to learn standing before walking

Why

Previous config caused either:

1. Harmonic oscillation (pelvic thrusts) from over-rigid waist
2. Instant collapse (ragdoll) from under-rigid waist
3. Unstable squat spawn position

This version should allow the robot to first learn to stand, then walk.

Full Changelog: v2.0.0...v2.1.0