Do not store `bad_files` & `hashfield` in `sites.json`

Because these make `sites.json` too bloat, and slow down whole client.
There should be stored in `content.db` instead.

Start by locating the code that writes and reads sites.json, bad_files, hashfield, and content.db; the issue names no specific files or tests. Trace how these values are used across the client before deciding the migration scope. Done means bad_files and hashfield are no longer stored in sites.json, are stored in content.db, and the client retains its behavior without the reported bloat.

Written by the indexing model from the issue text.