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/instrument/editor_session.cpp

@@ -72,7 +72,7 @@ void ReaSamplerEditor::refreshFromBank() {
     monoTrigger_ = processor_->monoTrigger();
     // A refresh that emptied the selection closes the curve popup — an open-but-invisible
     // modal would otherwise swallow clicks on the empty state.
-    if (selectedId_.empty()) curvePopup_ = CurveTarget::kNone;
+    if (selectedId_.empty()) closeCurvePopup();
     // Drop a filter that names a bank no longer present.
     if (!activeFilterBankId_.empty()) {
         bool found = false;