fix(scanner): split comma-joined ABS sidecar genres into separate tags

Audiobookshelf-style exports join genres into one comma-string
(["Epic, Action & Adventure, Military, Sword & Sorcery"]). The
smart-genre picker already split candidates for the genre column,
but the tags assembly used the raw unsplit array — so the whole
string landed as ONE element of media_items.tags and rendered as a
single tag everywhere.

Use pickSmartGenre's split candidates for tags too, exactly as the
function's own comment documents ('split parts included stay in
tags'). Commas inside a single subject heading remain legal within
one tag (EPUB dc:subject path unchanged).

internal/services/media_scanner.go

@@ -1884,11 +1884,17 @@ func extractAudiobookshelfSidecar(path string) *MediaMetadata {
 	}
 
 	// Smart genre (A2c §2.5): most-specific canonical genre wins the genre
-	// column; every candidate (split parts included) stays in tags.
-	if genre, _ := pickSmartGenre(sidecar.Genres); genre != "" {
+	// column; every candidate (split parts included) stays in tags. The
+	// split is the point: ABS-style exports join genres into one
+	// comma-string ("Epic, Action & Adventure, Military") which must land
+	// as separate tags, while commas inside a single subject heading stay
+	// legal within one tag.
+	genre, all := pickSmartGenre(sidecar.Genres)
+	if genre != "" {
 		metadata.Genre = genre
 	}
-	if tags := append(append([]string{}, sidecar.Genres...), sidecar.Tags...); len(tags) > 0 {
+	tags := append(append([]string{}, all...), sidecar.Tags...)
+	if len(tags) > 0 {
 		metadata.Tags = utils.NormalizeTags(tags)
 	}
 	if sidecar.Language != nil {