binpatch benchmark: multi-pair median over single-pair

Chose 8-pair median benchmark over single 0.38→0.39 pair because user noted the latest Sentry CLI release was an outlier and patches in general are smaller. Pairs: 0.29→0.30, 0.30→0.31, 0.32→0.33, 0.33→0.34, 0.35→0.36, 0.36→0.37, 0.37→0.38, 0.38→0.39. Aggregate: median 4.0%, mean 4.2%, min 0.9%, max 8.1%, avg 31.4MB gz / 1.32MB patch (95.8% saved). Display median case on homepage, range in caption. Methodology: should use HEAD for sizes instead of full download (efficiency-first); script still downloads. Bench script bench/sentry-cli-bench.mjs deleted per user request — numbers baked into SVG caption only.