My project pdot^1 has a full-ERD mode but it's honestly less useful than the semi-interactive/contextual mode of navigating schema subgraphs in a database of any size. pdot can output mermaid and render other graphs too, like trigger cascades and grant inheritance.
Supply chains in the sense of a centralized (or multi-centralized) logistics no, supply chains in the sense of mobile pastoral groups supporting armies' further extension yes. These did not stretch all the way back to central Asia. Groups like the White and Blue hordes, which later combined into the Golden Horde, were basically autonomous within the territory allotted them by the Qaghan -- they mostly owed the central authority a share of spoils, support for the postal system (örtöö or yam), and their presence when convened on matters of state. Armies would bring limited supplies with them as they campaigned, replacement horses and some small livestock, while the main group continued to focus on caring for the bulk of their herds. While not actively expanding their borders, steppe nomads usually moved between relatively well-established seasonal camps rather than continuously roaming.
It went offline earlier this year, but <https://web.archive.org/web/20220330034214/http://www.databa...> is something similar too. Diagrams not copy-pastable DDL, but at least for me the value is in seeing how other people have approached similar modeling problems, not in copying down their solutions -- so diagrams are perfect.
Ask! Create an issue if there's a tracker or send a short email explaining what you want to do and see if they're open to the idea, have more questions, or aren't interested in supporting it. No need to overthink formalities (although a quick "thanks for xyz" never hurt anyone's feelings), just be polite and concise.
Postgres schema comments (COMMENT ON COLUMN mytable.mycolumn IS 'spline reticulation coefficient'). Otherwise, I've given up on ever maintaining data model documentation and generate ad hoc graphs from different perspectives in the foreign key network: https://di.nmfay.com/exploring-databases-visually
I can't tell you whether you'll love or hate Fyodor Sologub's The Petty Demon but you won't feel lukewarm on it. The Cioran translation is more complete but harder to find than older translations now in the public domain.
I've been meaning to get to Victor Pelevin's The Life of Insects for a while.
^1 https://gitlab.com/dmfay/pdot