Widen noise detector offset from ±100Hz to ±200Hz to reduce spectral
leakage into the noise reference, and scale threshold_multiplier for
SNR space (2.8 → 1.54) so real CW signals reliably trigger tone
detection instead of producing all-E's at 60 WPM.
Fix misleading "decoder startup" timeout message on stop requests and
increase stop timeout from 2.2s to 5s.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>