You are given two tables: `users` - `user_id` BIGINT PRIMARY KEY - `signup_ts` TIMESTAMP `user_events` - `user_id` BIGINT - `event_ts` TIMESTAMP - `event_name` VARCHAR `user_events.user_id` references `users.user_id`. Assume all timestamps are stored in UTC. Define a user's **cohort month** as `DATE_TRUNC('month', signup_ts)`. A user is considered **retained** in month `n` if they generate at least one event in the calendar month that is `n` months after their cohort month. Ignore any events that occur before the user's `signup_ts`. Write SQL to compute **monthly cohort-based retention**. Return one row per `cohort_month` and `month_number` with the following columns: - `cohort_month` - `month_number` - `cohort_size`: number of distinct users who signed up in that cohort month - `retained_users`: number of distinct users from that cohort with at least one event in that month number - `retention_rate`: `retained_users / cohort_size` Your result should support month 0, 1, 2, ... retention analysis.