feat(web): add TanStack Query helpers for library endpoints

qk.{artists,artist,album} key generators and create*Query wrappers
with shared page size, sort-aware keys, and infinite-query plumbing
for /api/artists.

web/src/lib/api/queries.test.ts

@@ -0,0 +1,17 @@
+import { describe, expect, test } from 'vitest';
+import { qk } from './queries';
+
+describe('qk key generators', () => {
+  test('artists key includes sort discriminator', () => {
+    expect(qk.artists('alpha')).toEqual(['artists', { sort: 'alpha' }]);
+    expect(qk.artists('newest')).toEqual(['artists', { sort: 'newest' }]);
+  });
+
+  test('artist key tuple', () => {
+    expect(qk.artist('abc')).toEqual(['artist', 'abc']);
+  });
+
+  test('album key tuple', () => {
+    expect(qk.album('xyz')).toEqual(['album', 'xyz']);
+  });
+});

web/src/lib/api/queries.ts

@@ -0,0 +1,41 @@
+import { createQuery, createInfiniteQuery } from '@tanstack/svelte-query';
+import { api } from './client';
+import type { ArtistRef, ArtistDetail, AlbumDetail, Page } from './types';
+
+export type ArtistSort = 'alpha' | 'newest';
+export const ARTIST_PAGE_SIZE = 50;
+
+export const qk = {
+  artists: (sort: ArtistSort) => ['artists', { sort }] as const,
+  artist:  (id: string)       => ['artist', id] as const,
+  album:   (id: string)       => ['album', id] as const,
+};
+
+export function createArtistsQuery(sort: ArtistSort) {
+  return createInfiniteQuery({
+    queryKey: qk.artists(sort),
+    queryFn: ({ pageParam = 0 }) =>
+      api.get<Page<ArtistRef>>(
+        `/api/artists?sort=${sort}&limit=${ARTIST_PAGE_SIZE}&offset=${pageParam}`
+      ),
+    initialPageParam: 0,
+    getNextPageParam: (last) => {
+      const loaded = last.offset + last.items.length;
+      return loaded >= last.total ? undefined : loaded;
+    },
+  });
+}
+
+export function createArtistQuery(id: string) {
+  return createQuery({
+    queryKey: qk.artist(id),
+    queryFn: () => api.get<ArtistDetail>(`/api/artists/${id}`),
+  });
+}
+
+export function createAlbumQuery(id: string) {
+  return createQuery({
+    queryKey: qk.album(id),
+    queryFn: () => api.get<AlbumDetail>(`/api/albums/${id}`),
+  });
+}