Port to blueprint

src/window.blp

@@ -0,0 +1,40 @@
+using Gtk 4.0;
+using Adw 1;
+
+template $MusicusWindow : Adw.ApplicationWindow {
+  default-width: 600;
+  default-height: 300;
+
+  Box {
+    orientation: vertical;
+
+    HeaderBar header_bar {
+      [end]
+      MenuButton {
+        icon-name: "open-menu-symbolic";
+        menu-model: primary_menu;
+      }
+    }
+
+    Label label {
+      label: "Hello, World!";
+      vexpand: true;
+      styles ["title-1"]
+    }
+  }
+}
+
+menu primary_menu {
+  item {
+    label: "_Preferences";
+    action: "app.preferences";
+  }
+  item {
+    label: "_Keyboard Shortcuts";
+    action: "app.help-overlay";
+  }
+  item {
+    label: "_About Musicus";
+    action: "app.about";
+  }
+}