Function is_audible 

fn is_audible(peak: f32) -> bool

Pure decision shared by both audio-output probes: is a measured peak amplitude loud enough to be real playback? One threshold so the macOS tap (#233) and the Windows peak meter (#234) judge “audible” identically instead of drifting apart behind two copies. Pure, so it’s unit-tested without FFI on every OS (like media_key_pause_allowed just above).