pub fn init(explicit: Option<Tz>) -> Result<(), AppError>Expand description
Initializes the global timezone.
explicit — value from the --tz CLI flag (already parsed).
If explicit is None, tries SQLITE_GRAPHRAG_DISPLAY_TZ, then UTC.
Subsequent calls are silently ignored (OnceLock semantics).
Returns an error only if explicit is None and the env var is invalid.