fix: resolve Windows Unicode encoding errors in PDF builds

- Add PYTHONUTF8=1 env var to all Windows Docker run commands (PEP 540)
- Fix generate_figure_list.py to explicitly use encoding='utf-8' in
  write_text() instead of relying on system default (cp1252 on Windows)
- The ≈ character (\u2248) in Vol I content triggered charmap codec errors

book/quarto/scripts/mit_press/generate_figure_list.py

@@ -392,7 +392,7 @@ def main():
     # Write to output directory
     output_path = output_dir / 'FIGURE_LIST.txt'
     output_path.parent.mkdir(parents=True, exist_ok=True)
-    output_path.write_text('\n'.join(lines))
+    output_path.write_text('\n'.join(lines), encoding='utf-8')
     
     print(f"[Figure List] Written: {output_path}", file=sys.stderr)
     print(f"[Figure List] Total: {len(merged)} figures", file=sys.stderr)