fix: close review findings on the velocity-curve deck and bipolar curves

Cancels the curve-node drag whenever the popup closes so Esc mid-drag can't alias the amp curve; generalizes CurveTarget routing to one switch; fixes stale/overstated comments; clamps a pre-v12 depth fold; adds deck-inertness and filter-fold test coverage.

src/shell/panel/draw_kit.cpp

@@ -214,14 +214,15 @@ void drawButton(LICE_IBitmap* bmp, const KitButtonBox& button, const char* label
                    radius, toLice(borderCol), drawAlpha(borderCol), 0, true);
 
     if (label && *label) {
-        // Active fill is the accent — label goes in bg/base for contrast; else text/primary.
-        const Role textRole = (state == InteractionState::Active)
-                                  ? Role::BgBase
-                                  : Role::TextPrimary;
-        text(bmp, b, label, Font::Label, textRole, Align::Center);
+        text(bmp, b, label, Font::Label, buttonLabelRole(state), Align::Center);
     }
 }
 
+Role buttonLabelRole(InteractionState state) {
+    // Active fill is the accent — the mark goes in bg/base for contrast; else text/primary.
+    return state == InteractionState::Active ? Role::BgBase : Role::TextPrimary;
+}
+
 void drawSlider(LICE_IBitmap* bmp, const SliderGeometry& geom, InteractionState state) {
     if (!bmp || geom.track.empty()) return;