feat(web): add TanStack Query client singleton

Tuned defaults: retry disabled (we throw typed errors), 30s staleTime
to make tab-switch re-navigation feel instant, no refetchOnWindowFocus
(users on a music app don't expect spurious network when they tab back).

web/src/lib/query/client.ts

@@ -0,0 +1,11 @@
+import { QueryClient } from '@tanstack/svelte-query';
+
+export const queryClient = new QueryClient({
+  defaultOptions: {
+    queries: {
+      retry: false,
+      staleTime: 30_000,
+      refetchOnWindowFocus: false
+    }
+  }
+});