新增: 相册展示模块（左侧幻灯片+进度条+目录选择）

- 左侧固定卡片展示照片幻灯片，淡入淡出切换
- 进度条动画显示当前照片剩余时间
- 设置窗口支持选择图片目录和切换间隔(5/10/15/20/30/60秒)
- Win32 SHBrowseForFolderW 目录选择对话框
- Go 端管理幻灯片状态，按间隔推送照片 data URI

dialog.go

@@ -12,6 +12,13 @@ var (
 	comdlg32             = windows.NewLazySystemDLL("comdlg32.dll")
 	procGetOpenFileNameW  = comdlg32.NewProc("GetOpenFileNameW")
 	procChooseColorW      = comdlg32.NewProc("ChooseColorW")
+
+	shell32                 = windows.NewLazySystemDLL("shell32.dll")
+	procSHBrowseForFolderW  = shell32.NewProc("SHBrowseForFolderW")
+	procSHGetPathFromIDListW = shell32.NewProc("SHGetPathFromIDListW")
+
+	ole32dll          = windows.NewLazySystemDLL("ole32.dll")
+	procCoTaskMemFree = ole32dll.NewProc("CoTaskMemFree")
 )
 
 func slicePtr(s interface{}) uintptr {
@@ -117,3 +124,34 @@ func colorPickerDialog(owner uintptr, initialColor string) string {
 	b := (cc.rgbResult >> 16) & 0xFF
 	return fmt.Sprintf("#%02x%02x%02x", r, g, b)
 }
+
+func browseForFolderDialog(owner uintptr) string {
+	title, _ := windows.UTF16PtrFromString("选择图片目录")
+	var displayName [260]uint16
+
+	bi := struct {
+		HwndOwner      uintptr
+		PidlRoot       uintptr
+		PszDisplayName uintptr
+		LpszTitle      uintptr
+		UlFlags        uint32
+		LpFn           uintptr
+		LParam         uintptr
+		IImage         int32
+	}{
+		HwndOwner:      owner,
+		PszDisplayName: uintptr(unsafe.Pointer(&displayName[0])),
+		LpszTitle:      uintptr(unsafe.Pointer(title)),
+		UlFlags:        0x00000001 | 0x00000040,
+	}
+
+	pidl, _, _ := procSHBrowseForFolderW.Call(uintptr(unsafe.Pointer(&bi)))
+	if pidl == 0 {
+		return ""
+	}
+	defer procCoTaskMemFree.Call(pidl)
+
+	var path [260]uint16
+	procSHGetPathFromIDListW.Call(pidl, uintptr(unsafe.Pointer(&path[0])))
+	return windows.UTF16ToString(path[:])
+}