Get User Stats Timeseries

Per-day rolling DAU/WAU/MAU/stickiness over the selected lookback (admin).

Distinct (user, day) activity is read once over the lookback plus a 30-day seed, then the rolling windows are computed in Python so every output day is fully populated. When exclude_admins is set, Quadrillion staff are left out. Buckets use date_trunc over UTC timestamps.