Function system_tz 

pub fn system_tz() -> TimeZone

Read the host’s local timezone from the OS (TZ env var, then /etc/localtime) and resolve it in jiff’s tzdb.

Falls back to TimeZone::UTC when the OS zone can’t be determined — the same degraded default as [crate::wasm::browser_local_tz], its wasm twin. Call once at the composition root (e.g. CCC’s Session); do not sample it per render site (that would reintroduce the ambient-authority leak the clock port exists to prevent).