feat(theme): dual light/dark mode with Apple light theme, toggle, and theme-aware viewers

feat(export): add downloads to ADMET, MD, pairwise, AlphaFold, docking, pathway, plus 4 new learn topics

Refine design system: semantic color tokens, tiered motion, denser result cards, VinaLog toolbar

feat: add PNG/TSV/JSON/CSV/FASTA export to all 8 tool components