The search results were a chorus of ghosts. Forum posts from 2011, their images long since replaced by blue question mark icons. A GameFAQs guide written in all-caps by a user named “xX_Slayer_Xx.” Buried in the fourth result, a single, clean answer:
: Your graphics and control settings are typically located in the same parent directory:
If you are switching to a new PC, simply copy this folder over. No need to fiddle with Steam Cloud or account IDs. Happy demon hunting.