Submit thumbs-up or thumbs-down feedback for a profile returned by a search.

To identify the result being rated, copy these values from a completed /v2/search
response:

1. thread_id to chat_thread_id;
2. uuid to search_call_uuid;
3. search_results[].profile.linkedin_slug to linkedin_slug.

The specified search call must belong to the thread and be completed. The profile
must also be present in the thread's current completed ranking. When feedback is
saved, Pearch stores the profile as it appeared in that ranking together with a
high-freshness snapshot of the profile.

Ratings are keyed on the chat thread, never on the per-call uuid of a search
response: reopening a thread serves the cached ranking but returns a new uuid,
so keying on it would lose the feedback. search_call_uuid records the individual
API interaction from which the rating was submitted; cached interactions resolve
through the thread's completed search state.

A rating belongs to the thread rather than to its author: there is one rating per
(chat_thread_id, linkedin_slug), and re-submitting updates it even when a
different user submits it. author_type records whether the last submitter was a
human, an agent, or both, and is overwritten together with the rating.

reason is optional and is typically provided for downvotes. On an update, omitting
it keeps the existing reason when the rating is unchanged and clears the reason when
the rating changes. A blank or null reason is treated like an omitted reason.

String values are trimmed; rating and author_type are case-insensitive. Unknown
request fields are rejected.