refactor: 按模块重构项目结构

- 删除 vars 全局状态，按职责拆分 internal/ 包：scanner/probe/classify/organize/mover/store/digest
- 数据驱动归类规则替代图片/视频重复分支，store 改为结构体实例
- build.sh 按系统类型编译：Windows 用 upx 压缩，macOS/Linux 不压缩
- 忽略目录拆分：图片_已忽略 / 视频_已忽略
- 输出构建产物加入 .gitignore

internal/classify/classify.go

@@ -0,0 +1,72 @@
+// Package classify 提供纯函数的分辨率归类规则，不依赖任何状态。
+package classify
+
+import "strings"
+
+// Orientation 画面方向
+type Orientation int
+
+const (
+	OrientationSquare Orientation = iota
+	OrientationHorizontal
+	OrientationVertical
+)
+
+// OrientationOf 由宽高判定画面方向
+func OrientationOf(width, height int) Orientation {
+	switch {
+	case width > height:
+		return OrientationHorizontal
+	case width < height:
+		return OrientationVertical
+	default:
+		return OrientationSquare
+	}
+}
+
+func (o Orientation) String() string {
+	switch o {
+	case OrientationHorizontal:
+		return "横屏"
+	case OrientationVertical:
+		return "竖屏"
+	default:
+		return "等比"
+	}
+}
+
+// ImageDir 返回图片归类子目录名，如 "图片_横屏_1080P" / "图片_GIF"
+func ImageDir(ext string, width, height int) string {
+	if strings.EqualFold(ext, ".gif") {
+		return "图片_GIF"
+	}
+	return resolutionDir("图片", ext, width, height)
+}
+
+// VideoDir 返回视频归类子目录名，如 "视频_竖屏_4k" / "视频_横屏_GIF"
+func VideoDir(ext string, width, height int) string {
+	return resolutionDir("视频", ext, width, height)
+}
+
+func resolutionDir(kind, ext string, width, height int) string {
+	ori := OrientationOf(width, height).String()
+	if strings.EqualFold(ext, ".gif") {
+		return kind + "_" + ori + "_GIF"
+	}
+	if suffix := matchStandard(width, height); suffix != "" {
+		return kind + "_" + ori + "_" + suffix
+	}
+	overflow := "原图"
+	if kind == "视频" {
+		overflow = "原画质"
+	}
+	return kind + "_" + ori + "_" + levelName(longEdge(width, height), overflow)
+}
+
+// longEdge 返回长边像素
+func longEdge(w, h int) int {
+	if w > h {
+		return w
+	}
+	return h
+}