-- drop unique index to allow multiple entries (e.g. same token across
-- device logins) for a single user.  the application already keeps tokens
-- tidy by unregistering on sign-out, so duplicates are harmless.

drop index if exists fcm_tokens_user_token_idx;

-- maintain a regular index on user_id for performance
create index if not exists fcm_tokens_user_idx on public.fcm_tokens(user_id);