Build panel in SQL; run causal regression

Task 1 — build the panel in SQL Take 2025-09-01 (UTC) as the current date. Using the four tables described below, assemble a user-day panel that covers every calendar date d from 2025-08-25 through 2025-09-01 inclusive. Emit a row for a user_id on date d only when d is not earlier than that user's signup_date, which guarantees signup_age_days is never negative. Return exactly the following columns, in this order: d (DATE) — the calendar date of the row. user_id (INT).…