feat: launcher-style search UI (Raycast/Spotlight)

- Replace Pagefind UI with cmdk + Pagefind low-level API
- Quick actions when empty: nav (home, blog, tags) + recent posts
- Debounced full-text search with keyboard navigation
- Pass recent posts from layout to SearchModal
- Extract cn utility to lib/utils.ts
- Remove Pagefind UI styles, add Radix overlay styling
- Align blog search bar styling with launcher

Co-authored-by: Cursor <cursoragent@cursor.com>

components/layout-shell.tsx

@@ -9,10 +9,15 @@ const BackToTop = dynamic(() => import('./back-to-top').then(mod => ({ default:
   ssr: false,
 });
 
-export function LayoutShell({ children }: { children: React.ReactNode }) {
+interface LayoutShellProps {
+  children: React.ReactNode;
+  recentPosts?: { title: string; url: string }[];
+}
+
+export function LayoutShell({ children, recentPosts = [] }: LayoutShellProps) {
   return (
     <div className="flex min-h-screen flex-col">
-      <SiteHeader />
+      <SiteHeader recentPosts={recentPosts} />
       <main className="flex-1 container mx-auto px-4 py-6">
         {children}
       </main>