cathar v0.7.4

Tape / VHS restoration chain and measured de-hum / de-plosive fixes
(#25).

Added

• Tape / VHS restoration chain (#25)
  — cathar vhs runs a gated cascade: DC block, rumble high-pass, stereo
  azimuth + bass-mono, declip (only if flat-top runs are present), dropout
  inpaint, declick, decrackle, adaptive dehum, event-gated deplosive, coherent
  spectral subtraction from the quietest 4 s, multiband de-ess. Library:
  vhs_restore, VhsOptions. Inspired by the measured
  auto_pure_linear stages in
  AI Hybrid VHS Audio Restorer.
• detect_mains_hz — pick 50 vs 60 from the recording's quiet spectrum.
• learn_noise_print_quietest — noise print from the quietest N seconds.
• remove_dc — mean subtraction (DC blocking).

Changed

• dehum --adaptive — each harmonic is cancelled at the frequency it
  actually sits (tape lines land 1–8 Hz off the exact series); 50 vs 60 is
  taken from the recording when the other series is clearly stronger;
  harmonics that do not stand out are skipped, so no-hum files pass through
  unchanged. --freq 0 auto-detects. Envelope bandwidth widens with harmonic
  number; a 6 dB cap over the running envelope keeps a voiced partial parked
  on a mains line from being taken with it.
• deplosive — default is now event-gated (--method events): a blast
  under 150 Hz that stands over the low band's running level and leads the
  mid band is taken down, and nothing else is touched. Undamaged material is
  bit-identical. --method transients keeps the legacy whole-file STFT path,
  which was measured harmful on controls.