[feat] support minimizing to the system tray on Linux when closing

src/gui/tray/linux_tray.h

@@ -0,0 +1,40 @@
+/*
+ * @Author: DI JUNKUN
+ * @Date: 2026-06-23
+ * Copyright (c) 2026 by DI JUNKUN, All Rights Reserved.
+ */
+
+#ifndef _LINUX_TRAY_H_
+#define _LINUX_TRAY_H_
+
+#if defined(__linux__) && !defined(__APPLE__)
+
+#include <cstdint>
+#include <memory>
+#include <string>
+
+struct SDL_Window;
+
+namespace crossdesk {
+
+struct LinuxTrayImpl;
+
+class LinuxTray {
+ public:
+  LinuxTray(::SDL_Window* app_window, const std::string& tooltip,
+            int language_index, uint32_t exit_event_type);
+  ~LinuxTray();
+
+  bool MinimizeToTray();
+  void RemoveTrayIcon();
+  void ProcessEvents();
+
+ private:
+  std::unique_ptr<LinuxTrayImpl> impl_;
+};
+
+}  // namespace crossdesk
+
+#endif  // defined(__linux__) && !defined(__APPLE__)
+
+#endif  // _LINUX_TRAY_H_