Fix embed use-after-free, restore golden fixture + refs tests, drop dead note_entry

src/core/instrument/ui/envelope_overlay.h

@@ -1,7 +1,8 @@
 // envelope_overlay.h — amp-envelope -> polyline geometry for the Sample-view envelope overlay.
 // Engine-free by design (no sample_map/sampler_core dependency); mirror of waveform_view /
-// param_slider. The shell packs the zone's AdsrSeconds/TriggerParams into AmpEnvelope and draws
-// the polyline plus a handle at each node (envelope_edit does the hit-test).
+// param_slider. The shell packs the one parameter set's AdsrSeconds/TriggerParams into
+// AmpEnvelope and draws the polyline plus a handle at each node (envelope_edit does the
+// hit-test).
 
 #pragma once