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/CMakeLists.txt

@@ -85,7 +85,7 @@ if(WIN32 AND EXISTS "${VST3_SDK}/public.sdk/source/main/pluginfactory.cpp")
         capture_browser keyboard_strip sample_bands sample_chrome
         waveform_view bank_sync browser_scroll param_slider tooltip
         theme component_geometry bank_grid trigger_seam envelope_overlay envelope_edit
-        knob_deck curve_popup master_gain sample_usage file_bytes)
+        knob_deck deck_groups curve_popup master_gain sample_usage file_bytes)
     # SDK_INC gives the REAPER VST3 interfaces + API header for the bridge; WDL_INC gives
     # LICE for the editor. The VST3 SDK headers arrive via vst3_sdk PUBLIC.
     target_include_directories(reasampler_vst PRIVATE ${REASAMPLER_SRC_DIR} ${SDK_INC} ${WDL_INC})