instrument: one VELOCITY deck for all three velocity curves, bipolar and off by default for pitch and filter

Payload v12 appends the new velocity->pitch curve and folds the retired filter velAmount into its now-bipolar curve, so pre-v12 projects reopen sounding identical. Preview button takes a drawn play triangle.

src/shell/instrument/reasampler_editor.h

@@ -86,6 +86,9 @@ private:
     // spelling.
     using OverlayEnv = instrument::ui::OverlayEnv;
 
+    // Which of the three velocity curves a deck cell edits — also the popup's open state.
+    using CurveTarget = instrument::ui::CurveTarget;
+
     // Controls on the setup surface. The int value is the opaque control id the pure
     // knob_deck hit-test returns; the shell maps it to the one parameter set or a
     // processor-side per-instance setter. The id space and the deck's group composition are
@@ -120,7 +123,6 @@ private:
         kCurveNode,       // a velocity-curve control point (index = point index)
         kVelKnob,         // the chrome preview-velocity radial knob
         kStripKey,        // a piano-strip key (index = MIDI note); carries the name tooltip
-        kCurveButton,     // the chrome mini curve-preview button (opens the popup)
         kPopupClose,      // the curve popup's Close (x) button
     };
     struct HoverTarget {
@@ -159,11 +161,12 @@ private:
     // label<->value swap on hover/drag.
     void paintDeck(LICE_IBitmap* bmp, const FaceLayout& fl);
 
-    // The mini curve-preview button (chrome) and the modal curve editor it summons.
-    void paintCurveButton(LICE_IBitmap* bmp, const Rect& r);
+    // A deck cell's mini curve thumbnail (the VELOCITY group) and the modal editor it summons.
+    void paintCurveButton(LICE_IBitmap* bmp, const Rect& r, CurveTarget target, bool disabled,
+                          bool hovered);
     void paintCurvePopup(LICE_IBitmap* bmp, int w, int h);
-    // The velocity->amp transfer-curve editor (X = velocity 0-127, Y = amp 0-1); its only
-    // host is the popup sheet. `r` empty -> draws nothing.
+    // The velocity transfer-curve editor (X = velocity 0-127, Y = the curve's own domain); its
+    // only host is the popup sheet. `r` empty -> draws nothing.
     void paintVelocityCurve(LICE_IBitmap* bmp, const Rect& r);
     // Traces the amp-envelope overlay + its draggable node handles over `waveArea`, ONCE at
     // full band height (never per lane).
@@ -456,8 +459,13 @@ private:
     // delta from this anchor, so a grab never jumps the value.
     double dragKnobStartValue_ = 0.0;
 
-    // Curve popup open flag, never persisted.
-    bool curvePopupOpen_ = false;
+    // Which velocity curve the popup is editing; kNone = closed. Never persisted.
+    CurveTarget curvePopup_ = CurveTarget::kNone;
+    // The parameter-set curve `curvePopup_` names. Both overloads exist because every edit
+    // path needs the mutable one and paint needs the const one; routing through this ONE
+    // switch is what keeps the three curves on a single popup/draw/hit-test code path.
+    VelocityCurve& editedCurve();
+    const VelocityCurve& editedCurve() const;
 
     // Peak-thumbnail cache (mirror of bank_panel), keyed by "id|binCount" so a resize
     // recomputes at the new width. Cleared on refresh so a stale sample never shows.