feat: add feature UI components with useQuery hooks

- navigation: SiteHeader component + useHeader hook
- blog: ArticleCard, ArticleList, ArticleDetail + useArticleList,
  useArticleBySlug hooks
- marketing-pages: PageHero, PageContent + usePageBySlug,
  useSiteSettings hooks
- App pages now thin server wrappers that prefetch + hydrate;
  feature components own their data fetching via useSuspenseQuery

packages/marketing-pages/src/ui/hooks/use-page-by-slug.ts

@@ -0,0 +1,12 @@
+"use client";
+
+import { useSuspenseQuery } from "@tanstack/react-query";
+import { useTRPC } from "@repo/core-trpc";
+import type { Page } from "../../entities/models/page";
+
+export function usePageBySlug(slug: string) {
+  const trpc = useTRPC();
+  return useSuspenseQuery(
+    trpc.marketingPages.pageBySlug.queryOptions({ slug }),
+  ) as { data: Page | null };
+}