feat: 扫描整理并行化、WebSocket 实时进度与统计看板

- 移动阶段并行处理文件，按原子计数上报累计进度
- 扫描遍历阶段实时上报已发现文件数，界面不再卡在 0/0
- 新增 /api/scan/ws WebSocket 实时推送扫描状态；前端断线指数退避自动重连，并以低频轮询兜底
- 新增统计看板与媒体库筛选/排序，目录选择器路径不存在时回退到最近可用父目录
- 存放目录支持自定义并持久化，默认输出到 KMP已整理

internal/probe/brightness.go

@@ -18,9 +18,9 @@ const (
 	// brightnessDecodeLimit 明暗分析允许解码的最大像素数，超出时跳过分析（按 mid 归类），避免超大图 OOM
 	brightnessDecodeLimit = 40_000_000
 	// thumbnailMaxEdge 明暗分析时大图缩放后的最长边像素，缩小到该尺寸内再统计
-	thumbnailMaxEdge = 512
+	thumbnailMaxEdge = 256
 	// thumbnailScaleThreshold 像素数超过该值才缩放为缩略图再统计
-	thumbnailScaleThreshold = 1_000_000
+	thumbnailScaleThreshold = 250_000
 )
 
 // AnalyzeBrightness 打开并解码图片，分析明暗程度。
@@ -78,6 +78,7 @@ func scaleToThumbnail(img image.Image, maxEdge int) image.Image {
 
 // analyzeBrightness 统计暗色/亮色像素占比（ITU-R BT.601 亮度公式）。
 // 完全透明的像素（alpha=0）不计入统计。
+// 对常见内存布局（NRGBA/RGBA/Gray）直接访问像素数组，避免 image.At 接口逐像素开销。
 func analyzeBrightness(img image.Image) (darkScore float64, lightScore float64) {
 	bounds := img.Bounds()
 	totalPixels := bounds.Dx() * bounds.Dy()
@@ -85,23 +86,70 @@ func analyzeBrightness(img image.Image) (darkScore float64, lightScore float64)
 		return 0, 0
 	}
 
-	darkCount, lightCount, sampleCount := 0, 0, 0
-	for y := bounds.Min.Y; y < bounds.Max.Y; y++ {
-		for x := bounds.Min.X; x < bounds.Max.X; x++ {
-			r, g, b, a := img.At(x, y).RGBA()
-			if a == 0 {
-				continue
+	var darkCount, lightCount, sampleCount int64
+	switch m := img.(type) {
+	case *image.NRGBA:
+		pix := m.Pix
+		for y := bounds.Min.Y; y < bounds.Max.Y; y++ {
+			offset := m.PixOffset(bounds.Min.X, y)
+			for x := bounds.Min.X; x < bounds.Max.X; x++ {
+				r, g, b, a := pix[offset], pix[offset+1], pix[offset+2], pix[offset+3]
+				if a == 0 {
+					offset += 4
+					continue
+				}
+				countBrightness(float64(r), float64(g), float64(b), &darkCount, &lightCount)
+				sampleCount++
+				offset += 4
 			}
-			r8 := uint8(r >> 8)
-			g8 := uint8(g >> 8)
-			b8 := uint8(b >> 8)
-			brightness := 0.299*float64(r8) + 0.587*float64(g8) + 0.114*float64(b8)
-			if brightness < 80 {
-				darkCount++
-			} else if brightness > 175 {
-				lightCount++
+		}
+	case *image.RGBA:
+		pix := m.Pix
+		for y := bounds.Min.Y; y < bounds.Max.Y; y++ {
+			offset := m.PixOffset(bounds.Min.X, y)
+			for x := bounds.Min.X; x < bounds.Max.X; x++ {
+				// 预乘 alpha：若完全不透明则按直接值，否则近似取非预乘分量
+				a := pix[offset+3]
+				if a == 0 {
+					offset += 4
+					continue
+				}
+				r, g, b := pix[offset], pix[offset+1], pix[offset+2]
+				if a != 255 {
+					r = uint8(int(r) * 255 / int(a))
+					g = uint8(int(g) * 255 / int(a))
+					b = uint8(int(b) * 255 / int(a))
+				}
+				countBrightness(float64(r), float64(g), float64(b), &darkCount, &lightCount)
+				sampleCount++
+				offset += 4
+			}
+		}
+	case *image.Gray:
+		pix := m.Pix
+		for y := bounds.Min.Y; y < bounds.Max.Y; y++ {
+			offset := m.PixOffset(bounds.Min.X, y)
+			for x := bounds.Min.X; x < bounds.Max.X; x++ {
+				v := float64(pix[offset])
+				if v < 80 {
+					darkCount++
+				} else if v > 175 {
+					lightCount++
+				}
+				sampleCount++
+				offset++
+			}
+		}
+	default:
+		for y := bounds.Min.Y; y < bounds.Max.Y; y++ {
+			for x := bounds.Min.X; x < bounds.Max.X; x++ {
+				r, g, b, a := img.At(x, y).RGBA()
+				if a == 0 {
+					continue
+				}
+				countBrightness(float64(r>>8), float64(g>>8), float64(b>>8), &darkCount, &lightCount)
+				sampleCount++
 			}
-			sampleCount++
 		}
 	}
 
@@ -110,3 +158,13 @@ func analyzeBrightness(img image.Image) (darkScore float64, lightScore float64)
 	}
 	return float64(darkCount) / float64(sampleCount), float64(lightCount) / float64(sampleCount)
 }
+
+// countBrightness 按 BT.601 亮度公式累计暗/亮像素计数
+func countBrightness(r, g, b float64, darkCount, lightCount *int64) {
+	brightness := 0.299*r + 0.587*g + 0.114*b
+	if brightness < 80 {
+		*darkCount++
+	} else if brightness > 175 {
+		*lightCount++
+	}
+}