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/include/RenderFxJob.h

@@ -55,6 +55,12 @@ int run_open_fx_gui(const std::string& jobPath);
 // --open-fx-gui.
 int run_fx_gui_server(const std::string& jobPath);
 
+// Capture the GUI plugin's current state (component + controller) as base64
+// of the bridge blob [4B BE compLen][comp][4B BE ctrlLen][ctrl] - the same
+// format applyPreset accepts. Runs on the GUI pump thread; blocks up to
+// timeoutMs. outB64 stays empty on timeout or when the plugin has no state.
+void fxGuiRequestCapture(void* hwnd, std::string& outB64, int timeoutMs);
+
 // Realtime FX chain (T2.4): live VST3 audio effects on the bridge master mix.
 // setChain() is async (a worker thread loads the plugins and swaps the chain);
 // process() runs ONLY on the audio thread; shutdown() joins the worker and must