[studio] Complete drag/drop support for files

src/olympic/studio/modlib/include/studio/dragdrop.hpp

@@ -0,0 +1,22 @@
+/*
+ * Copyright 2016 - 2025 Gary Talent (gary@drinkingtea.net). All rights reserved.
+ */
+
+#pragma once
+
+#include <ox/std/string.hpp>
+#include <ox/model/def.hpp>
+
+namespace studio {
+
+struct FileRef {
+	static constexpr auto TypeName = "net.drinkingtea.studio.FileRef";
+	static constexpr auto TypeVersion = 1;
+	ox::String path;
+};
+
+OX_MODEL_BEGIN(FileRef)
+	OX_MODEL_FIELD(path)
+OX_MODEL_END()
+
+}

src/olympic/studio/modlib/include/studio/imguiutil.hpp

@@ -63,6 +63,7 @@ auto dragDropSource(auto const&cb) noexcept {
 		if (ig::DragDropSource const tgt; tgt) [[unlikely]] {
 			return cb();
 		}
+		return ox::Error{};
 	} else {
 		if (ig::DragDropSource const tgt; tgt) [[unlikely]] {
 			cb();

src/olympic/studio/modlib/include/studio/studio.hpp

@@ -6,6 +6,7 @@
 
 #include <studio/configio.hpp>
 #include <studio/context.hpp>
+#include <studio/dragdrop.hpp>
 #include <studio/editor.hpp>
 #include <studio/filedialog.hpp>
 #include <studio/imguiutil.hpp>