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/src/SharedMemoryIPC.cpp

@@ -23,6 +23,19 @@ ShmHandle* shm_open(const char* name) {
     if (!h->view) { CloseHandle(h->map); delete h; return nullptr; }
     return h;
 }
+// Creates the mapping (used by tests/self-check; the DAW normally owns it).
+ShmHandle* shm_create(const char* name) {
+    ShmHandle* h = new ShmHandle();
+    int wlen = MultiByteToWideChar(CP_UTF8, 0, name, -1, nullptr, 0);
+    std::wstring wname(wlen, L'\0');
+    MultiByteToWideChar(CP_UTF8, 0, name, -1, &wname[0], wlen);
+    h->map = CreateFileMappingW(INVALID_HANDLE_VALUE, nullptr, PAGE_READWRITE, 0,
+                                sizeof(SharedAudioBufferIPC), wname.c_str());
+    if (!h->map) { delete h; return nullptr; }
+    h->view = MapViewOfFile(h->map, FILE_MAP_ALL_ACCESS, 0, 0, sizeof(SharedAudioBufferIPC));
+    if (!h->view) { CloseHandle(h->map); delete h; return nullptr; }
+    return h;
+}
 void shm_close(ShmHandle* h) {
     if (!h) return;
     if (h->view) UnmapViewOfFile(h->view);