fix(ui): hide Comic/Manga editor section for non-comics media

The metadata editor's Comic/Manga section (Manga Type, Reading
Direction, Age Rating, Story Arc, Imprint, Scan Info, Metadata
Notes, B&W) rendered for every item — an audiobook showed a manga
dropdown, which is nonsense.

MediaDetail now carries LibraryTypeName (resolved via
GetLibraryType in the /media/:uuid handler) and a
ShowComicMetadata() gate: comics and manga libraries always show the
section; other media only when the scanner recorded comic-style
values (fixed-layout manga-style EPUBs get those scanner defaults
deliberately — when present they stay editable).

internal/handlers/media_detail.go

@@ -12,6 +12,11 @@ import (
 type MediaDetail struct {
 	database.MediaItems // Embedded - ALL book fields available
 
+	// Display type of the owning library ("audiobooks", "comics", "ebooks",
+	// "manga"); "" when it could not be resolved. Drives media-type-aware
+	// UI gating (e.g. hiding the Comic/Manga editor section).
+	LibraryTypeName string
+
 	// Audio editorial/tech surfaces (A2a): duration parsed out of the
 	// audio_metadata JSONB the scanner wrote (display-only).
 	audioDurationSeconds float64
@@ -44,6 +49,18 @@ type MediaDetail struct {
 	DeletedAnnotations []DeletedAnnotationResponse `json:"deleted_annotations"`
 }
 
+// ShowComicMetadata reports whether the Comic/Manga section belongs on
+// this item's edit modal: comics and manga libraries always; other media
+// only when the scanner actually recorded comic-style values (fixed-layout
+// manga-style EPUBs get scanner defaults).
+func (md *MediaDetail) ShowComicMetadata() bool {
+	if md.LibraryTypeName == "comics" || md.LibraryTypeName == "manga" {
+		return true
+	}
+	return (md.MangaType.Valid && md.MangaType.String != "") ||
+		(md.ReadingDirection.Valid && md.ReadingDirection.String != "")
+}
+
 // BookStatsData is the per-book reading-stats card payload.
 type BookStatsData struct {
 	TotalMinutes int