POST /admin/realms/{realm}/users silently drops the `id` field on
Keycloak 26.x. Switch user creation in seed-keycloak.sh to
POST /admin/realms/{realm}/partialImport, which preserves the pinned
id (verified by round-trip). This restores deterministic UUIDs for
alice/bob/carlos/diana and unblocks downstream consumers that depend
on stable `sub` claims (FedWiki owner.json references, demo seeder
person rows).