Quality plot renderer (per-frame plot + heatmap strip + rate-quality curve, dependency-free SVG)

A dependency-free (pure standard-library) Python companion that renders the article's three pictures from measurement output, without computing any metric itself (FFmpeg/libvmaf does that; the convex-hull and BD-rate MATH lives in 5.3's convex-hull-plotter.py). It reads per-frame scores from libvmaf JSON, libvmaf CSV, or ffmpeg-quality-metrics JSON, auto-detecting the dialect and the requested metric (vmaf/psnr/ssim/ms_ssim). --per-frame FILE renders a per-frame line plot on the metric's FULL ra