chore(template): clean-slate template snapshot from bb4a0c7

Curated, product-agnostic snapshot of the post-story-04 tree: demo
content deleted, auth-only reference feature, web-next shell, all gates
green. Product-specific docs, ADRs 027-029, PRDs/epics/archive, editor
library traces, and product naming are curated out; generic template
repairs (coverage provider devDeps, root test:coverage script, live
lint fixes, root-only release-please) are kept. See TEMPLATE.md for
provenance, curation list, and usage.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016j8z4VHjedXDTjEDNg7qHK

packages/core-trpc/src/query-client.ts

@@ -0,0 +1,22 @@
+import { QueryClient } from "@tanstack/react-query";
+
+let clientQueryClient: QueryClient | undefined;
+
+const defaultOptions = {
+  queries: {
+    staleTime: 30 * 1000,
+    refetchOnWindowFocus: false,
+  },
+};
+
+export function getQueryClient(): QueryClient {
+  if (typeof window === "undefined") {
+    // Server: always create a new instance per request
+    return new QueryClient({ defaultOptions });
+  }
+  // Browser: singleton
+  if (!clientQueryClient) {
+    clientQueryClient = new QueryClient({ defaultOptions });
+  }
+  return clientQueryClient;
+}