Content API

We should add an auth token column to users and assign everyone a random token that allows them to authenticate over an API to fetch their content.
- [x] Add auth token to users
- [x] Generate random tokens for all existing users
- [x] Set randomized tokens on user creation
- [ ] Add API endpoints for universes, characters, locations, and items that return each by ID, requiring the owner's auth token if they are private
- [ ] Add API endpoints to list a user's content (universes/characters/locations/items) ids+names+descriptions, serving back all content if their auth token is passed, and only their private content otherwise.

This API would go a long way to developing apps on top of the notebook, like #54

No files, tests, or entry points are identified in the issue. Start by defining the API contract for item lookup and user-content listing, including private-content authorization and response fields. Done means all four content types support the requested ID and listing endpoints with the stated token behavior.

Written by the indexing model from the issue text.