fix(saas): SQL type cast fixes for E2E relay flow

- key_pool.rs: cast cooldown_until to timestamptz for comparison with NOW()
- key_pool.rs: cast request_count to bigint (INT4→INT8) for sqlx decoding
- service.rs: cast cooldown_until to timestamptz in quota sort query
- scheduler.rs: cast last_seen_at to timestamptz in device cleanup
- totp.rs: use DateTime<Utc> instead of rfc3339 string for updated_at

crates/zclaw-saas/src/scheduler.rs

@@ -89,7 +89,7 @@ pub fn start_db_cleanup_tasks(db: PgPool) {
         loop {
             interval.tick().await;
             match sqlx::query(
-                "DELETE FROM devices WHERE last_seen_at < $1"
+                "DELETE FROM devices WHERE last_seen_at::timestamptz < $1"
             )
             .bind({
                 let cutoff = (chrono::Utc::now() - chrono::Duration::days(90));