collab: Route `search_channel_members` through Cloud (#56465)

This PR makes it so we route the `UserService::search_channel_members`
call through Cloud instead of hitting the database.

This is the last of the calls to be routed through Cloud. We'll clean up
the old database-backed implementations in a follow-up PR.

Closes CLO-746.

Release Notes:

- N/A
b13cb40b97Marshall Bowers committed on 5/12/2026, 1:05:19 PM· committed by GitHubparenta130674
2 files changedLine totals unavailable