feat: add gallery app for viewing/testing

gallery/main.cpp

@@ -0,0 +1,23 @@
+#include <QGuiApplication>
+#include <QLoggingCategory>
+#include <QQmlApplicationEngine>
+
+#include <QtQml/QQmlExtensionPlugin>
+Q_IMPORT_QML_PLUGIN(DesignSystemPlugin)
+
+int main(int argc, char *argv[])
+{
+  QGuiApplication app(argc, argv);
+
+  QQmlApplicationEngine engine;
+  QObject::connect(
+      &engine, &QQmlApplicationEngine::objectCreationFailed, &app, []() { QCoreApplication::exit(-1); },
+      Qt::QueuedConnection);
+
+  // https://doc.qt.io/qt-6/qtqml-writing-a-module.html#eliminating-run-time-file-system-access
+  engine.addImportPath(":/live.flowy/imports");
+
+  engine.loadFromModule("Gallery", "Main");
+
+  return app.exec();
+}