palette: give the spectral mid and the envelope trace their own roles

Decouples the keyboard strip's mid stop from accent/secondary, which the
deep-teal darkening had inverted. Adds overlay/trace (#816AA6), the first
value to clear 3:1 against the waveform. Replaces the frozen-premise test.

src/shell/instrument/editor_paint_waveform.cpp

@@ -25,11 +25,9 @@ using audio::computeEnvelope;
 
 namespace {
 // Marker roles — semantic, drawn through the kit's palette: start AND loop start/end both
-// = teal (secondary). Loop markers moved off tertiary/purple so the loop span + bars no
-// longer share a role with the envelope overlay trace, which owns tertiary exclusively in
-// this region (measured RGB was identical: #C2AAE8 for both). Secondary-vs-primary contrast
-// here measures 1.12:1, below tertiary's 1.37:1 — accepted deliberately: markers are bars
-// and a span fill, not the 1px trace that pairing was moved off of.
+// = teal (secondary). Markers are 2px bars and a 20%-alpha span fill, not the 1px trace, so
+// they live with 1.92:1 against the waveform; the trace, which cannot, has its own role.
+// Do not collapse the two back onto one role — they overlap in this rect.
 constexpr Role kRoleStartMarker = Role::AccentSecondary;
 constexpr Role kRoleLoopMarker  = Role::AccentSecondary;
 }  // namespace
@@ -114,10 +112,8 @@ void ReaSamplerEditor::paintEnvelopeOverlay(LICE_IBitmap* bmp, const OverlayArea
     const StageEnvelope env = packEnvelope(overlayEnv_, params_.play, frames, startFrame);
     const std::vector<EnvVertex> poly = buildEnvelopePolyline(env, waveArea, totalSeconds);
 
-    // Trace the polyline in the categorical TERTIARY accent (purple): the waveform behind it is
-    // drawn in the primary lime, and the secondary teal this used to use sits too close to that
-    // hue to separate from it. Clip x to the wave rect. Knots are handles, not line vertices.
-    const LICE_pixel line = toLice(roleColor(Role::AccentTertiary));
+    // Clip x to the wave rect. Knots are handles, not line vertices.
+    const LICE_pixel line = toLice(roleColor(Role::OverlayTrace));
     const EnvVertex* prev = nullptr;
     for (const EnvVertex& v : poly) {
         if (v.knot) continue;
@@ -132,7 +128,7 @@ void ReaSamplerEditor::paintEnvelopeOverlay(LICE_IBitmap* bmp, const OverlayArea
     // accent-hot when this node is the grabbed one. Every vertex is guaranteed in-bounds; the
     // handle is additionally clamped inside the band so one on an edge node never overhangs
     // into the neighbouring bands.
-    const LICE_pixel handle = toLice(roleColor(Role::AccentTertiary));
+    const LICE_pixel handle = toLice(roleColor(Role::OverlayTrace));
     const LICE_pixel handleHot = toLice(roleColor(Role::AccentHot));
     for (const EnvVertex& v : poly) {
         if (v.node == EnvNode::Origin || v.node == EnvNode::ReleaseEnd) continue;