fix(db): add missing revoked_at column to refresh_tokens

backend/migrations/000008_add_refresh_tokens_revoked_at.down.sql

@@ -0,0 +1,2 @@
+DROP INDEX IF EXISTS idx_refresh_tokens_revoked_at;
+ALTER TABLE refresh_tokens DROP COLUMN IF EXISTS revoked_at;

backend/migrations/000008_add_refresh_tokens_revoked_at.up.sql

@@ -0,0 +1,2 @@
+ALTER TABLE refresh_tokens ADD COLUMN revoked_at TIMESTAMPTZ;
+CREATE INDEX idx_refresh_tokens_revoked_at ON refresh_tokens(revoked_at);