feat: Consolidate and subdivide rules

[MikkelPaulson]

This is a draft implementation of #463 for review and discussion. See the parent issue for the schema proposal.

To do:

• Migrate data to new schema
• Update API & docs (I presume)
• Add test coverage to detect orphans, circular references, and contradictory parent/child relationships
• Delete Python script before merging (included for discussion)

[bagelbits]

I think that looks good if you want to go forward with the rest.