Research: Create an ER diagram to describe DB tables for posts, collections, and authors

[fennifith]

For all the necessary properties, see PostInfo.ts, CollectionInfo.ts, and PersonInfo.ts

Not all of this needs an individual database column; e.g. roles, achievements, socials could be stored in JSONB.

Some of these will need additional tables to define relations; author to post is many-to-many, so we'll need a PostAuthor table to store the authors of each post.

PostInfo and CollectionInfo should also include columns for the raw post markdown.