Update wan21_wan22_comparison: full 256/256 venhancer coverage (web-safe re-encoded)

Re-encode all mp4s (Main profile, no B-frames, faststart, SAR 1:1) + autoplay HTML

Add wan21_wan22_comparison: 256 SpatialVID-HD scenes, 5 refiners (baseline / Wan2.1-VGC / Wan2.2-VGC / SeedVR2 / VEnhancer v2)