Fix master volume + VST3FX GUI state restore on save/reload

- serializeProjectToSchema now writes master volume_db and mastering gui_open_path/name
- deserialize restores masterVolume + masteringSettings.gui_open_path/name
- track vst_gui_open_path/name fallback to live state (not just _persistFxGui*)
- MasteringModal/FXRackModal reopen effects react to isOpen + restored gui path
- openMasterVstGui/openVstGui store gui name for reopen
- bridge: /preset capture endpoint + RenderFxJob.captureState for GUI knob state

native_bridge/src/FxGuiServer.cpp

@@ -11,6 +11,7 @@
 //   POST /input           -> {type:"mousedown|mousemove|mouseup|wheel|keydown|keyup",
 //                             x,y,button,deltaY,keyCode} -> PostMessage to HWND
 //   POST /close           -> detach + exit 0
+//   GET  /preset          -> {"preset_b64":"..."} current plugin state
 //
 // The HTTP server runs on a worker thread; the calling (STA) thread runs the
 // message pump — VST3 editors need COM apartment + pump on the same thread.
@@ -44,6 +45,7 @@
 // Defined in RenderFxJob.cpp (global scope); declared here outside the
 // anonymous namespace so both TUs see the same symbol.
 extern void fxGuiRequestResize(HWND hwnd, int w, int h);
+extern void fxGuiRequestCapture(void* hwnd, std::string& outB64, int timeoutMs);
 
 namespace {
 
@@ -575,6 +577,11 @@ void runHttpServer(HWND hwnd, std::atomic<bool>& stop) {
                              SWP_NOMOVE | SWP_NOSIZE | SWP_NOACTIVATE | SWP_SHOWWINDOW);
             }
             sendResponse(c, 200, "application/json", "{\"ok\":true}", 11);
+        } else if (req.path == "/preset") {
+            std::string b64;
+            fxGuiRequestCapture(hwnd, b64, 1500);
+            const std::string body = "{\"preset_b64\":\"" + b64 + "\"}";
+            sendResponse(c, 200, "application/json", body.data(), (int)body.size());
         } else if (req.path == "/close") {
             sendResponse(c, 200, "application/json", "{\"ok\":true}", 11);
             stop.store(true);