Place cover and artist images in library folders on upload import

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

services/api/internal/uploads/sidecar_test.go

@@ -0,0 +1,26 @@
+package uploads
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestSidecarDirs(t *testing.T) {
+	tpl := "{albumartist}/{year} - {album}/{disc:1-}{track:02} - {title}.{ext}"
+	album, artist := sidecarDirs(tpl, "Artist/2020 - Album/01 - Song.flac")
+	require.Equal(t, "Artist/2020 - Album", album)
+	require.Equal(t, "Artist", artist)
+
+	album, artist = sidecarDirs("{albumartist}/{album}/{disc:1}/{track:02} - {title}.{ext}", "A/B/1/01 - S.flac")
+	require.Equal(t, "A/B", album)
+	require.Equal(t, "A", artist)
+
+	album, artist = sidecarDirs("{albumartist} - {album}/{title}.{ext}", "A - B/S.flac")
+	require.Equal(t, "A - B", album)
+	require.Empty(t, artist)
+
+	album, artist = sidecarDirs("{albumartist} - {title}.{ext}", "A - S.flac")
+	require.Empty(t, album)
+	require.Empty(t, artist)
+}