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/ui/app.go

@@ -119,6 +119,11 @@ type appState struct {
 	lastActivity time.Time
 	locked       bool
 	lockDialog   *passwordDialog
+
+	// tray owns the system-tray icon and (when minimize_to_tray is on)
+	// the WM_CLOSE subclass. nil on platforms or installs where it
+	// could not be set up.
+	tray *trayRuntime
 }
 
 // snapshotEntries returns a freshly serialized slice of config entries.
@@ -174,6 +179,17 @@ func loop(w *app.Window, configPath string) error {
 	state.registerAllHotkeys()
 	go state.runHotkeyLoop(w)
 
+	// Install the system tray icon + close-hook (Windows only). HWND
+	// discovery races the very first FrameEvent, so kick it from a
+	// goroutine that polls FindWindow for a few hundred ms.
+	_, _, _, minToTray := state.store.Preferences()
+	go func() {
+		tr := installTrayRuntime(i18n.T("app_title"), minToTray, w.Invalidate)
+		state.mu.Lock()
+		state.tray = tr
+		state.mu.Unlock()
+	}()
+
 	// Tick once per second to refresh TOTP codes.
 	go func() {
 		t := time.NewTicker(time.Second)
@@ -188,6 +204,7 @@ func loop(w *app.Window, configPath string) error {
 		switch e := w.Event().(type) {
 		case app.DestroyEvent:
 			global.Log.WithField("func", fn).Info("window closed")
+			state.tray.Stop()
 			return e.Err
 		case app.FrameEvent:
 			gtx := app.NewContext(&ops, e)
@@ -436,8 +453,8 @@ func drawFrame(gtx layout.Context, th *material.Theme, st *appState, w *app.Wind
 			case settingsActionImportLegacy:
 				st.importDialog = newImportLegacyDialog()
 			case settingsActionPreferences:
-				lang, theme, autoLock, _ := st.store.Preferences()
-				st.prefsDialog = newPreferencesDialog(lang, normalizeThemeMode(theme), autoLock)
+				lang, theme, autoLock, minToTray := st.store.Preferences()
+				st.prefsDialog = newPreferencesDialog(lang, normalizeThemeMode(theme), autoLock, minToTray)
 			case settingsActionAbout:
 				st.aboutDialog = newAboutDialog()
 			}
@@ -450,11 +467,17 @@ func drawFrame(gtx layout.Context, th *material.Theme, st *appState, w *app.Wind
 	if st.prefsDialog != nil {
 		return st.prefsDialog.Layout(gtx, th, func(r preferencesResult) {
 			if !r.cancel {
-				_, _, _, minToTray := st.store.Preferences()
-				st.store.SetPreferences(r.language, string(r.theme), r.autoLockMinutes, minToTray)
+				_, _, _, prevMinToTray := st.store.Preferences()
+				st.store.SetPreferences(r.language, string(r.theme), r.autoLockMinutes, r.minimizeToTray)
 				i18n.SetLanguage(r.language)
 				st.themeMode = r.theme
 				st.theme = nil // force rebuild on next frame
+				// Re-arm or release the WM_CLOSE hook when the user
+				// flips the minimize-to-tray preference. Hot-reloading
+				// avoids forcing a restart for a setting change.
+				if prevMinToTray != r.minimizeToTray && st.tray != nil {
+					st.tray.setMinimizeToTray(r.minimizeToTray)
+				}
 			}
 			st.prefsDialog = nil
 			w.Invalidate()