refactor(bridge): split fx bridge, stabilize VST3 host chain, drop old install engines

- remove diagnostic canaries from audio hot path (crackle fix) and
  stuck C5 note raw-MIDI test (Vst2Instrument::init noteOff)
- split native bridge into daw_vst_bridge (VSTi) + fx_vst_bridge (VST FX)
- VST3: processData prepare before setActive, zero input buses, accept
  both .vstpreset and bridge-state blob in RenderJob presets
- native_render/vst_engine: bridge-exe discovery + render_fx_chain + /fx-gui
- delete old install/ engine binaries (install via sidecar+resources now)
- add BUILD_LAYOUT.md, build_selfcheck, tools/ diagnostics

native_bridge/CMakeLists.txt

@@ -98,6 +98,32 @@ else()
   target_link_libraries(daw_vst_bridge PRIVATE ${FLUIDSYNTH_LIBRARIES} ${SFIZZ_LIBRARIES})
 endif()
 
+# ── fx_vst_bridge: VST FX host (split from daw_vst_bridge). Windows-only:
+#    one-shot modes --render-fx / --scan / --open-fx-gui / --fx-gui. No SHM
+#    realtime loop (the live master FX chain stays in daw_vst_bridge because
+#    it processes the instrument mix in-process). ──
+if(WIN32)
+add_executable(fx_vst_bridge
+  src/main_fx.cpp
+  src/RenderFxJob.cpp
+  src/FxGuiServer.cpp
+)
+if(VST3_SDK_TARGET)
+  target_compile_definitions(fx_vst_bridge PRIVATE HAVE_VST3SDK=1)
+  target_link_libraries(fx_vst_bridge PRIVATE ${VST3_SDK_TARGET} sdk_hosting sdk_common)
+  target_sources(fx_vst_bridge PRIVATE
+    ${CMAKE_CURRENT_SOURCE_DIR}/vst3sdk/public.sdk/source/vst/hosting/module_win32.cpp
+    ${CMAKE_CURRENT_SOURCE_DIR}/vst3sdk/public.sdk/source/common/memorystream.cpp
+  )
+endif()
+  find_package(JPEG REQUIRED)  # libjpeg-turbo (vcpkg) — FxGuiServer.cpp JPEG encode
+  # FX modes are VST3 + builtin DSP only — no fluidsynth/sfizz (avoids a
+  # runtime libfluidsynth-3.dll dependency for the FX bridge).
+  target_link_libraries(fx_vst_bridge PRIVATE JPEG::JPEG)
+  # Required Windows libs
+  target_link_libraries(fx_vst_bridge PRIVATE winmm imm32 ws2_32)
+endif()
+
 # ── gui_probe: standalone VST3 GUI attach probe (debug tool, not shipped) ──
 if(WIN32)
 add_executable(gui_probe