Fix output paths: all build scripts save to /app/repo/medal-solvers/optimized/

Update build_task285_scatter.py: use official neurogolf_utils.py for validation and scoring (8.818 pts confirmed)

Upload actual build_task285_scatter.py (265/265 pass, score 8.61 vs 5.98 = +2.63pts)

Add Task 285 optimized model builder (ScatterElements approach, 265/265 pass, score 8.61 vs 5.98 original = +2.63 pts)