feat(ui): 系统托盘 + 关闭最小化到托盘

- 原生 win32 实现的 TrayManager：Shell_NotifyIcon + 私有 message-only
  窗口承载 popup 菜单，专用 OS 线程跑 GetMessage 泵，避免引入 cgo 依赖。
- WindowSubclass 通过 SetWindowLongPtrW 子类化 Gio 主窗口，拦截
  WM_CLOSE：minimize_to_tray=true 时吞掉消息只隐藏窗口；exit 路径下
  放行让 Gio 正常关闭事件循环。
- Preferences 新增"最小化到托盘"复选框，切换后立即重装/卸载钩子，
  不需要重启程序。
- 托盘菜单提供 Show / Hide / Exit；左键单击图标等同 Show；右键弹菜单。
- 非 Windows 平台所有相关 API 退化为 ErrUnsupported / no-op stub。

internal/i18n/locales/de.toml

@@ -448,3 +448,20 @@ other = "Automatisch sperren nach (Minuten)"
 
 [hint_auto_lock_disabled]
 other = "0 deaktiviert. Nur wirksam, wenn die Konfiguration verschlüsselt ist."
+
+# --- System-Tray ---
+
+[tray_show]
+other = "WinAuth anzeigen"
+
+[tray_hide]
+other = "WinAuth ausblenden"
+
+[tray_exit]
+other = "Beenden"
+
+[label_minimize_to_tray]
+other = "Beim Schließen in den Tray minimieren"
+
+[hint_minimize_to_tray]
+other = "Schließen des Fensters versteckt es im System-Tray statt das Programm zu beenden."

internal/i18n/locales/en.toml

@@ -450,3 +450,20 @@ other = "Auto-lock after (minutes)"
 
 [hint_auto_lock_disabled]
 other = "Set to 0 to disable. Only takes effect when the configuration is encrypted."
+
+# --- System tray ---
+
+[tray_show]
+other = "Show WinAuth"
+
+[tray_hide]
+other = "Hide WinAuth"
+
+[tray_exit]
+other = "Exit"
+
+[label_minimize_to_tray]
+other = "Minimize to tray when closing the window"
+
+[hint_minimize_to_tray]
+other = "Closing the window hides it to the system tray instead of exiting."

internal/i18n/locales/zh-CN.toml

@@ -448,3 +448,20 @@ other = "自动锁定（分钟）"
 
 [hint_auto_lock_disabled]
 other = "填 0 关闭。仅当配置已加密时生效。"
+
+# --- 系统托盘 ---
+
+[tray_show]
+other = "显示 WinAuth"
+
+[tray_hide]
+other = "隐藏 WinAuth"
+
+[tray_exit]
+other = "退出"
+
+[label_minimize_to_tray]
+other = "关闭窗口时最小化到托盘"
+
+[hint_minimize_to_tray]
+other = "勾选后点击窗口关闭按钮将隐藏到系统托盘而非退出程序。"