feat: 增加 EXIF 旋转图片自动转正

- 解析 JPEG EXIF Orientation，方向 5/6/7/8 的竖拍横存图不再误入横屏目录
- 配置 ffmpeg 时用 ffmpeg 物理转正像素并保留原 EXIF；无 ffmpeg 时按显示方向归类
- 新增 ffmpeg.path / organize.rotateImages 配置项
- 补充 EXIF 解析与旋转幂等测试

internal/probe/exif_test.go

@@ -0,0 +1,103 @@
+package probe
+
+import (
+	"encoding/binary"
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+// buildJpegWithOrientation 拼一个带 Exif 方向标记的最小 JPEG：
+// SOI + APP1(Exif) + EOI，APP1 里只放 TIFF 头 + IFD0 一条 Orientation。
+func buildJpegWithOrientation(t *testing.T, orientation uint16, bigEndian bool) []byte {
+	t.Helper()
+	var order binary.ByteOrder = binary.LittleEndian
+	if bigEndian {
+		order = binary.BigEndian
+	}
+	bom := []byte("II")
+	if bigEndian {
+		bom = []byte("MM")
+	}
+	// TIFF 头(8) + IFD0 计数(2) + 一条目(12)
+	tiff := make([]byte, 0, 8+2+12)
+	tiff = append(tiff, bom...)
+	magic := make([]byte, 2)
+	order.PutUint16(magic, 42)
+	tiff = append(tiff, magic...)
+	ifdOff := make([]byte, 4)
+	order.PutUint32(ifdOff, 8)
+	tiff = append(tiff, ifdOff...)
+	count := make([]byte, 2)
+	order.PutUint16(count, 1)
+	tiff = append(tiff, count...)
+	// 一条目：tag=0x0112 type=SHORT count=1 value=orientation
+	entry := make([]byte, 12)
+	order.PutUint16(entry[0:2], 0x0112)
+	order.PutUint16(entry[2:4], 3) // SHORT
+	order.PutUint32(entry[4:8], 1) // count
+	order.PutUint16(entry[8:10], orientation)
+	tiff = append(tiff, entry...)
+
+	app1Data := append([]byte("Exif\x00\x00"), tiff...)
+	segLen := len(app1Data) + 2
+	out := []byte{0xFF, 0xD8} // SOI
+	out = append(out, 0xFF, 0xE1)
+	lenB := make([]byte, 2)
+	binary.BigEndian.PutUint16(lenB, uint16(segLen))
+	out = append(out, lenB...)
+	out = append(out, app1Data...)
+	out = append(out, 0xFF, 0xD9) // EOI
+	return out
+}
+
+func TestReadExifOrientation(t *testing.T) {
+	dir := t.TempDir()
+	cases := []struct {
+		name    string
+		ori     uint16
+		bigEnd  bool
+		want    int
+	}{
+		{"le6", 6, false, 6},
+		{"be8", 8, true, 8},
+		{"le1", 1, false, 1},
+	}
+	for _, c := range cases {
+		t.Run(c.name, func(t *testing.T) {
+			p := filepath.Join(dir, c.name+".jpg")
+			if err := os.WriteFile(p, buildJpegWithOrientation(t, c.ori, c.bigEnd), 0644); err != nil {
+				t.Fatal(err)
+			}
+			if got := ReadExifOrientation(p); got != c.want {
+				t.Fatalf("ReadExifOrientation = %d, want %d", got, c.want)
+			}
+		})
+	}
+
+	// 非 JPEG 返回 0
+	p := filepath.Join(dir, "notjpeg.txt")
+	if err := os.WriteFile(p, []byte("hello"), 0644); err != nil {
+		t.Fatal(err)
+	}
+	if got := ReadExifOrientation(p); got != 0 {
+		t.Fatalf("non-jpeg ReadExifOrientation = %d, want 0", got)
+	}
+	// 不存在的文件返回 0
+	if got := ReadExifOrientation(filepath.Join(dir, "missing.jpg")); got != 0 {
+		t.Fatalf("missing ReadExifOrientation = %d, want 0", got)
+	}
+}
+
+func TestNeedsDimensionSwap(t *testing.T) {
+	cases := map[int]bool{
+		1: false, 2: false, 3: false, 4: false,
+		5: true, 6: true, 7: true, 8: true,
+		0: false, 9: false,
+	}
+	for ori, want := range cases {
+		if got := NeedsDimensionSwap(ori); got != want {
+			t.Fatalf("NeedsDimensionSwap(%d) = %v, want %v", ori, got, want)
+		}
+	}
+}