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/core/instrument/ui/deck_groups.cpp

@@ -238,6 +238,36 @@ bool overlayEnvInert(OverlayEnv env, bool pitchEnvEnabled, bool filterEnabled) {
     return false;  // unreachable for a valid enumerator; silences a warning.
 }
 
+bool deckKnobInert(DeckParam id, bool pitchEnvEnabled, bool filterEnabled) {
+    switch (id) {
+        case DeckParam::kPitchEnvAttack:
+        case DeckParam::kPitchEnvHold:
+        case DeckParam::kPitchEnvDecay:
+        case DeckParam::kPitchEnvDepth:
+            return !pitchEnvEnabled;
+        case DeckParam::kFilterMorph:
+        case DeckParam::kFilterCutoff:
+        case DeckParam::kFilterQ:
+        case DeckParam::kFilterDrive:
+        case DeckParam::kFilterModAmt:
+        case DeckParam::kFilterKeyTrack:
+        // The filter's velocity curve sits in the VELOCITY group but is a filter parameter:
+        // it goes inert with every other one, so no surface can reach a param the knobs can't.
+        case DeckParam::kFilterVelCurve:
+        case DeckParam::kFilterEnvAttack:
+        case DeckParam::kFilterEnvHold:
+        case DeckParam::kFilterEnvDecay:
+        case DeckParam::kFilterEnvSustain:
+        case DeckParam::kFilterEnvRelease:
+        case DeckParam::kFilterTrigAttack:
+        case DeckParam::kFilterTrigHold:
+        case DeckParam::kFilterTrigDecay:
+            return !filterEnabled;
+        default:
+            return false;
+    }
+}
+
 bool liveCommitFor(LiveDragKind kind, int paramId) {
     switch (kind) {
         case LiveDragKind::kDeckKnob: