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/tests/host.rs

@@ -114,6 +114,13 @@ fn effect_ports_state_latency_and_audio_lifecycle() {
         envelope
             .params
             .insert("sensitivity_1".into(), ParamValue::F32(-12.));
+        envelope
+            .params
+            .insert("threshold".into(), ParamValue::F32(6.));
+        envelope.params.insert("ratio".into(), ParamValue::F32(3.));
+        envelope
+            .params
+            .insert("knee".into(), ParamValue::String("hard".into()));
         let encoded = serde_json::to_vec(&envelope).unwrap();
         let mut framed = (encoded.len() as u64).to_le_bytes().to_vec();
         framed.extend_from_slice(&encoded);