Variable STEP_KEYFRAMESConst

Step keyframes defining weight transfer and foot placement

Four-phase step animation:

1. Frames 0-5: Weight shift to back foot (준비, Junbi - Preparation)
2. Frames 6-11: Front foot lift and extension (이동, Idong - Movement)
3. Frames 12-15: Front foot placement (착지, Chakji - Landing)
4. Frames 16-17: Weight settle and stabilize (안정, Anjeong - Stabilization)