UpdateClient never adds new OAuth2 credentials (duplicate add/update blocks) #54

File: core/csharp/MicroZen.Api/Services/ClientsGrpcService.cs (UpdateClient)

What this is: Mapping a request into updated Client + credentials.

Problem: The two credentialsToUpdate / credentialsToAdd blocks in UpdateClient are identical — both use the same Where(... existing.Any(... ClientId match ...)), so "add" can never add a genuinely new credential (it only keeps ones that already exist) and the two lists are always the same set. New credentials are silently dropped on update.

Fix: The "add" set should be credentials not already present (!client.OAuth2Credentials.Any(...)); the "update" set should be those present. Deduplicate the two near-copy projections into one helper.

If we skip it: Updating a client never adds new OAuth2 credentials.