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.

plugins/patina/plugin/src/lib.rs

@@ -105,6 +105,15 @@ impl Plugin for Patina {
                         state.gestures[i] = false;
                     }
                 }
+                if edited.knee != before.knee {
+                    let knee = match edited.knee {
+                        patina_core::Knee::Soft => params::KneeParam::Soft,
+                        patina_core::Knee::Hard => params::KneeParam::Hard,
+                    };
+                    setter.begin_set_parameter(&params.knee);
+                    setter.set_parameter(&params.knee, knee);
+                    setter.end_set_parameter(&params.knee);
+                }
                 if edited.bypass != before.bypass {
                     setter.begin_set_parameter(&params.bypass);
                     setter.set_parameter(&params.bypass, edited.bypass);