feat: add query provider for Tanstack

src/app/providers/QueryProvider.svelte

@@ -0,0 +1,17 @@
+<script lang="ts">
+/**
+ * Query Provider Component
+ *
+ * All components that use useQueryClient() or createQuery() must be
+ * descendants of this provider.
+ */
+import { queryClient } from '$shared/api/queryClient';
+import { QueryClientProvider } from '@tanstack/svelte-query';
+
+/** Slot content for child components */
+let { children } = $props();
+</script>
+
+<QueryClientProvider client={queryClient}>
+    {@render children?.()}
+</QueryClientProvider>

src/shared/api/queryClient.ts

@@ -0,0 +1,26 @@
+import { QueryClient } from '@tanstack/query-core';
+
+/**
+ * Query client instance
+ */
+export const queryClient = new QueryClient({
+    defaultOptions: {
+        queries: {
+            /**
+             * Default staleTime: 5 minutes
+             */
+            staleTime: 5 * 60 * 1000,
+            /**
+             * Default gcTime: 10 minutes
+             */
+            gcTime: 10 * 60 * 1000,
+            refetchOnWindowFocus: false,
+            refetchOnMount: true,
+            retry: 3,
+            /**
+             * Exponential backoff
+             */
+            retryDelay: attemptIndex => Math.min(1000 * 2 ** attemptIndex, 30000),
+        },
+    },
+});