Rewrite pepdiff paper with scientific tone and improved figure

- Remove promotional language, use neutral descriptive tone
- Clarify terminology: "Pooled across timepoints", "Log2 + impute + t-test (Perseus)"
- Add FDR (observed) column explanation in table caption
- New two-panel figure: (A) volcano by timepoint, (B) 24h with ground truth
- Add pairwise design example to supplementary
- Remove acknowledgements section, fix author field formatting

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: danmaclean