feat(patina): per-band compressor gain stage with Threshold, Ratio and Knee

Tester feedback asked for a threshold and a ratio. Each band now cuts like a
small compressor: Threshold (dB above the local floor) replaces Selectivity,
Ratio scales the cut per dB above it (inf:1 is the old behaviour), and a
Soft/Hard knee switch sets the curve. A small graph shows bump height in, cut
out. Mix and Output move to the slider panel so the detection panel fits.
common-ui gains rotary_text for knobs with custom value text.

website/src/data/plugins.ts

@@ -71,7 +71,7 @@ const COPY: Record<string, Copy> = {
       'Distortion chains build up harsh, ringing resonances. A static EQ cut takes out the tone along with the ring.',
     points: [
       'Finds ringing regions as they happen and pulls only those down.',
-      'Plain harmonic tone and transients pass; Selectivity sets what counts as harsh.',
+      'Each band works like a small compressor: Threshold sets what counts as harsh, Ratio how hard it is cut.',
       'Four focus points on the plot to cut more or protect a region.',
       'Delta monitoring to hear exactly what is removed.',
     ],