BIPH Mathematical Atlas — self-hosted font notices

Font binary files are provided without modification by the locked Fontsource packages.
Only the CSS font-display choice is customized; see src/styles/fonts.css.

@fontsource/source-serif-4 5.3.0: source-serif-4-OFL.txt
@fontsource/source-sans-3 5.3.0: source-sans-3-OFL.txt
@fontsource/ibm-plex-mono 5.3.0: ibm-plex-mono-OFL.txt
