domain: replace user-facing Jellyfin type badge with kind label (phase 3b)

The library detail page showed the raw Jellyfin item_type string
("MusicAlbum") to users. Add utils/mediaKind.ts with kindLabel(), a
presentation-only MediaKind -> human label map, and use it for the badge.
Flip the two remaining .type debug logs to .kind.

This removes the last user-visible Jellyfin vocabulary on the catalog
surface. primaryImageTag -> imageId rename (naming-only, ~40 sites across
catalog + player/merged types needing a Rust round-trip) intentionally
deferred as the lowest-value slice.

Frontend 644 tests, check clean.

src/lib/utils/mediaKind.ts

@@ -0,0 +1,31 @@
+// Presentation helpers for the neutral MediaKind.
+//
+// MediaKind is the app's provider-neutral item classification (defined in Rust,
+// generated into bindings). This module holds *display* concerns over it —
+// human-readable labels — which are presentation, not domain, and so live in
+// the frontend.
+
+import type { MediaKind } from "$lib/api/types";
+
+const KIND_LABELS: Record<MediaKind, string> = {
+  track: "Song",
+  album: "Album",
+  artist: "Artist",
+  playlist: "Playlist",
+  movie: "Movie",
+  series: "Series",
+  season: "Season",
+  episode: "Episode",
+  person: "Person",
+  channel: "Channel",
+  liveChannel: "Live TV",
+  channelItem: "Channel",
+  folder: "Folder",
+  other: "",
+};
+
+/** Human-readable label for a media kind (e.g. "Album"), or "" if unknown. */
+export function kindLabel(kind: MediaKind | null | undefined): string {
+  if (!kind) return "";
+  return KIND_LABELS[kind] ?? "";
+}