Every reference from a model to the record it belongs to is now
json:"-", so the webhook and target models (and the other parent and
child pairs in internal/database) can no longer marshal each other in
a loop. Preloading maps associations without reading json tags, so it
still fills these references; a new test preloads a webhook with its targets and
entrypoints and a target with its webhook, checks the references are
filled, and checks the marshalled JSON leaves them out.
Model: opus-5-5
