Bump plot cache-bust after updating two figures

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/src/components/datasets/protein/StaticDistributionPlots.tsx

@@ -1,7 +1,7 @@
 import React from 'react';
 
 const IMG_BASE = '/api/protein/plots';
-const CACHE_BUST = '?v=20260622';
+const CACHE_BUST = '?v=20260622b';
 
 const plots = [
   { name: 'Structure Similarity', file: 'Structure-similarity.png' },