-- DataMigration
-- Normalize existing usernames to lowercase so login becomes case-insensitive
-- (application code now always stores/looks up usernames lowercased). If two
-- users would collide after lowercasing, this UPDATE fails on the unique
-- constraint -- that's intentional: it surfaces a real conflict that needs
-- manual resolution rather than silently merging/dropping an account.
UPDATE "User" SET username = LOWER(username) WHERE username <> LOWER(username);