Service both VST3 parameter channels, and promote pitch key-track and Trigger length so all 44 ids issue

The SDK's own single-component sample drains inputParameterChanges in
process() and implements setParamNormalized; automation was reading the
GUI channel alone. The audio thread now patches a block it solely owns.

src/core/instrument/param/param_units.h

@@ -48,6 +48,17 @@ PlainRange plainRangeFor(DeckParam deck);
 double toPlain(DeckParam deck, double normalized);
 double toNormalized(DeckParam deck, double plain);
 
+// WHERE a control's value actually lives. The host's read and write paths branch on this, and
+// the exposed set is asserted against it: a control promoted into the list with no home would
+// otherwise no-op silently in BOTH directions, with nothing to catch it at compile time.
+enum class ValueHome {
+    None,             // not a scalar control at all — a toggle, a radio, a curve-popup cell
+    ParamSetNorm,     // the filter's four: the stored double IS the normalized position
+    ParamSet,         // every other knob the parameter set carries
+    InstanceScalar,   // beside the parameter set: master gain, and the pitch key-track scalar
+};
+ValueHome valueHomeFor(DeckParam deck);
+
 // The filter's four tone controls STORE their normalized position (payload v9), so their default
 // normalized value is that stored double verbatim and no taper participates in a host's
 // reset-to-default. Reporting Hz / Q / drive depth for them means CALLING their frozen laws, not