feat: run the per-voice filter between the pitch and amp stages, with its own deck

Params ride the one parameter set; payload v8 -> v9, off by default.
Deck composition moves to a pure deck_groups module in pitch -> filter -> amp order.

src/shell/instrument/editor_internal.h

@@ -1,8 +1,8 @@
 // editor_internal.h — shared helpers for the ReaSamplerEditor TU family. Included ONLY by
 // the editor's own shell TUs (editor_session / editor_controls / editor_paint_* /
 // editor_input_* / editor_platform) — never a public seam. Holds the Rect<->kit adapters,
-// small draw primitives (knob face / title band), label helpers, deck group ids, and the
-// velocity-curve box derivation. All inline.
+// small draw primitives (knob face / title band), label helpers, and the velocity-curve box
+// derivation. All inline.
 
 #pragma once
 
@@ -30,15 +30,6 @@
 
 namespace reasampler::vst {
 
-// Deck group ids (shell-owned; knob_deck treats them opaquely), left-to-right order.
-enum DeckGroup {
-    kGroupAmpEnv = 0,
-    kGroupPitch,
-    kGroupPitchEnv,
-    kGroupVoice,
-    kGroupMaster,
-};
-
 // Velocity-curve editor box metrics. The inset keeps node handles + the pick radius
 // inside the border so an endpoint at amp 0/1 stays grabbable; drag-off beyond
 // box+margin deletes the dragged node.