feat: Initialize Qt application with blank window

Co-authored-by: aider (gemini/gemini-2.5-pro) <aider@aider.chat>

src/main.cpp

@@ -0,0 +1,14 @@
+#include <QApplication>
+#include <QMainWindow>
+
+int main(int argc, char *argv[])
+{
+    QApplication app(argc, argv);
+
+    QMainWindow window;
+    window.setWindowTitle("OpenCAD");
+    window.resize(800, 600);
+    window.show();
+
+    return app.exec();
+}