fix: GUI VST native window qua bridge + audio path bridge (SF2 preview/play câm)

- open_vst_gui: bo WebviewWindowBuilder/thread, chi push_control type=4 (hwnd=0 -> bridge tao window)
- main.cpp: create_native_vst_window (class SonicForge_Native_VST3_Class, 800x600, khong TOPMOST),
  tao trong ChannelWorker job, map guiWindows, capture arg2 by value (fix dangling)
- app.jsx: guard isBridgeActive() 8 cho -> bridge active thi moi note di router -> pushEvent -> bridge
  (truoc day SF2 cam vi HAS_PYFLUIDSYNTH=FALSE -> /soundfont-render 501; VST3 path cu dung nativeSf/Carla)
- E2E: SF2 NOTE_ON qua dispatchMidiEvent -> SHM peak 0.029745; Nexus GUI native hwnd OK (license/preset)
- docs: TASKS.md + TEST_NOTES.md ghi batch fix + ket qua; gitignore vendor/junk

native_bridge/tests/shm_selfcheck.cpp

@@ -11,6 +11,11 @@
 int main() {
     // Use a test-only name to avoid clashing with a live DAW bridge.
     ShmHandle* h = shm_open("SonicForge_SelfCheck_IPC");
+#ifdef _WIN32
+    // On Windows the DAW (Rust) creates the mapping; standalone self-check
+    // creates it here when absent.
+    if (!h) h = shm_create("SonicForge_SelfCheck_IPC");
+#endif
     assert(h != nullptr);
 
     SharedAudioBufferIPC* ipc = shm_ptr(h);