3.6.0

🎵 Per-channel audio spectrograms

The spectrogram analyzer now handles multi-channel audio properly instead of
collapsing everything to mono up front.

Analysis

• Renders one annotated spectrogram per channel — labelled Left / Right
  for stereo, or Channel N — with the source channel layout preserved through
  ffmpeg (stereo stays stereo).
• Every plot is drawn by hand with Pillow: a frequency (Hz/kHz) Y axis, a time
  (s) X axis and a viridis dB colorbar, so each image is fully labelled and
  readable on its own.
• Finer frequency resolution (N_FFT 1024 → 2048); channels are capped at 6
  (extras noted), with a single mono-mixdown waveform alongside.

Display

• Spectrograms and the waveform now render full-width, one per row, instead
  of being squeezed into the 25% thumbnail grid — so the wide landscape plots
  are actually legible.

Docs & tests

• Updated the spectrogram wiki guide and analyzer tests for the per-channel output.

Full changelog: 3.5.1...3.6.0