Function format_utc_short 

pub fn format_utc_short(epoch_seconds: f64) -> String

Convert days since Unix epoch to (year, month, day). Format Unix seconds as MM-DD HH:MM:SS (UTC).

Exposed because report tables now show WHEN a series started and last moved, and the epoch value on its own is unreadable. Shares days_to_ymd with the session-id formatter rather than restating the calendar arithmetic; the year is omitted because these columns compare moments inside one run, where the month and day are already the widest useful distinction.