These are the types the per-resource extras and the activity endpoints
need, split out so they land before the code and tests that use them.
`MessageResponse` covers the `{"message": "..."}` body that the action
endpoints answer with, defaulting `message` so a reply carrying none still
decodes. `int_or_numeric_string` goes in alongside them: the spec calls
`frequency_id` a number, but a real 5.13.50 server sends the string `"5"`,
and a strict `i64` turned that into a hard decode error *after* the record
had already been created.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
