Add a Typography section to book setup with one-click preset pairings,
an advanced body/heading picker, and a live sample. Enumerate installed
fonts via a new list_system_fonts Tauri command (fontdb) so they appear
alongside the bundled set, with a note that system fonts may not embed
in exports.
Add EB Garamond, Lora, Source Serif 4, and Fraunces (OFL variable
fonts) and a font catalog with body/heading pairings. Store the chosen
fonts per book in BookSettings.fonts, defaulting to Literata so existing
books are unchanged.
pj