feat(web): add /settings page with ListenBrainz section

Adds api.put helper, ListenBrainz API module with query/mutation
helpers, a /settings route with token + enable/disable UI, and 5
tests. Adds Settings to the Shell nav.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

web/src/lib/api/client.ts

@@ -45,6 +45,8 @@ export const api = {
   get: <T>(path: string): Promise<T> => apiFetch(path) as Promise<T>,
   post: <T>(path: string, body: unknown): Promise<T> =>
     apiFetch(path, { method: 'POST', body: JSON.stringify(body) }) as Promise<T>,
+  put: <T>(path: string, body: unknown): Promise<T> =>
+    apiFetch(path, { method: 'PUT', body: JSON.stringify(body) }) as Promise<T>,
   del: (path: string): Promise<null> =>
     apiFetch(path, { method: 'DELETE' }) as Promise<null>
 };

web/src/lib/api/listenbrainz.ts

@@ -0,0 +1,44 @@
+import { createQuery, createMutation } from '@tanstack/svelte-query';
+import type { QueryClient } from '@tanstack/svelte-query';
+import { api } from './client';
+
+export type LBStatus = {
+  enabled: boolean;
+  token_set: boolean;
+  last_scrobbled_at: string | null;
+};
+
+export function getListenBrainzStatus(): Promise<LBStatus> {
+  return api.get<LBStatus>('/api/me/listenbrainz');
+}
+
+export function setListenBrainzToken(token: string): Promise<LBStatus> {
+  return api.put<LBStatus>('/api/me/listenbrainz', { token });
+}
+
+export function setListenBrainzEnabled(enabled: boolean): Promise<LBStatus> {
+  return api.put<LBStatus>('/api/me/listenbrainz', { enabled });
+}
+
+export const LB_QUERY_KEY = ['settings', 'listenbrainz'] as const;
+
+export function createLBStatusQuery() {
+  return createQuery({
+    queryKey: LB_QUERY_KEY,
+    queryFn: getListenBrainzStatus
+  });
+}
+
+export function createTokenMutation(queryClient: QueryClient) {
+  return createMutation<LBStatus, Error, string>({
+    mutationFn: (token: string) => setListenBrainzToken(token),
+    onSuccess: () => queryClient.invalidateQueries({ queryKey: LB_QUERY_KEY })
+  });
+}
+
+export function createEnabledMutation(queryClient: QueryClient) {
+  return createMutation<LBStatus, Error, boolean>({
+    mutationFn: (enabled: boolean) => setListenBrainzEnabled(enabled),
+    onSuccess: () => queryClient.invalidateQueries({ queryKey: LB_QUERY_KEY })
+  });
+}