e37316cef8
seedKnownUsers() inserted demo services with random UUIDs and no
idempotency guard, causing duplicates when the seed ran alongside or
after the main seed (which uses deterministic IDs + ON CONFLICT DO
UPDATE on id). The admin seed API had the same issue.
Now both paths use deterministic UUIDs with ON CONFLICT DO UPDATE on
id, making the upsert idempotent regardless of seed order or repetition.
Same pattern already used for clients (40143c4).
Co-Authored-By: Paperclip <noreply@paperclip.ing>