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/routes/library/[id]/+page.svelte

@@ -4,6 +4,7 @@
   import { page } from "$app/stores";
   import { goto } from "$app/navigation";
   import { navigateBack } from "$lib/utils/navigation";
+  import { kindLabel } from "$lib/utils/mediaKind";
   import { commands } from "$lib/api/bindings";
   import type { MediaItem, Library } from "$lib/api/types";
   import { library, libraryItems, isLibraryLoading, currentLibrary, libraries } from "$lib/stores/library";
@@ -402,8 +403,8 @@
 
           <!-- Metadata -->
           <div class="flex items-center gap-4 text-sm text-gray-400">
-            {#if item.type}
-              <span class="px-2 py-1 bg-[var(--color-surface)] rounded">{item.type}</span>
+            {#if kindLabel(item.kind)}
+              <span class="px-2 py-1 bg-[var(--color-surface)] rounded">{kindLabel(item.kind)}</span>
             {/if}
             {#if item.durationMs}
               <span>{formatDuration(item.durationMs)}</span>