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

src-tauri/src/lib.rs

@@ -697,7 +697,8 @@ pub fn run() {
                         .args(["/IM", "daw_engine.exe", "/T", "/F"])
                         .status();
                     let _ = std::process::Command::new("taskkill")
-                        .args(["/IM", "daw_vst_bridge.exe", "/T", "/F"])
+                        .args(["/IM", "daw_vst_bridge.exe", "/T", "/F",
+                        "/IM", "fx_vst_bridge.exe", "/T", "/F"])
                         .status();
                     window.app_handle().exit(0);
                 }

src-tauri/tauri.conf.json

@@ -27,7 +27,7 @@
       "binaries/libfluidsynth-3.dll": "libfluidsynth-3.dll",
       "binaries/jpeg62.dll": "jpeg62.dll"
     },
-    "externalBin": ["binaries/daw_vst_bridge"],
+    "externalBin": ["binaries/daw_vst_bridge", "binaries/fx_vst_bridge"],
     "windows": {
       "nsis": {
         "installerHooks": "hooks.nsh"