Add reviewer-driven paper fixes: figures, tables, and scripts

- Add paper figures (convergence, UMAP, LDA, GradCAM) to figures/ for Overleaf
- Regenerate convergence figure with larger font size (10→14) per reviewer R3-3
- Add age rows and MIMIC race rows to demographics table per reviewer R2-10/R2-11
- Add generate_lda_figure.py for proper 1D LDA density plot per reviewer R3-4
- Update generate_statistical_tables.py with age binarization support
- Fix UMAP script output filename to match LDA figure naming

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: sebasmos