schedule update on a recurring event reports success but changes nothing #951

Found while verifying #950 against local bc3 (run 20261022-215052-occurrence-urls, steps 003, 010 and 027).

basecamp schedule update <recurring-entry-id> --summary X prints "Updated" and exits 0, but nothing changes.

bc3's ensure_non_recurring_event answers PUT /schedule_entries/:id.json for a recurring event with a 302 to the first occurrence. The HTTP client follows the redirect as a GET, so UpdateEntry (schedule.go:787) receives an entry back and reports success. The bc3 log shows the PUT, the 302 and the GET, with no write.

So a user, or an agent following #950's hint to "pass the event's ID", is told the series was updated when it wasn't.

Suggested fix: treat a redirect on a write as a failure rather than following it. That belongs in the SDK, since no write should silently become a GET. The CLI can then report that bc3 doesn't allow API edits to a recurring event. It's worth checking whether other write endpoints redirect the same way.