feat: add Export ReClass XML and remove local-path tests

Adds Export ReClass XML menu item that writes NodeTree to ReClass .NET
compatible XML format with full round-trip fidelity. Removes test cases
that referenced local machine file paths.

src/mainwindow.h

@@ -47,6 +47,7 @@ private slots:
     void toggleMcp();
     void setEditorFont(const QString& fontName);
     void exportCpp();
+    void exportReclassXmlAction();
     void importFromSource();
     void importReclassXml();
     void showTypeAliasesDialog();