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/site-header.tsx

@@ -15,7 +15,11 @@ const SearchModal = dynamic(
   { ssr: false }
 );
 
-export function SiteHeader() {
+interface SiteHeaderProps {
+  recentPosts?: { title: string; url: string }[];
+}
+
+export function SiteHeader({ recentPosts = [] }: SiteHeaderProps) {
   const [isSearchOpen, setIsSearchOpen] = useState(false);
   const pages = allPages
     .slice()
@@ -93,6 +97,7 @@ export function SiteHeader() {
         <SearchModal
           isOpen={isSearchOpen}
           onClose={() => setIsSearchOpen(false)}
+          recentPosts={recentPosts}
         />
       </div>
     </header>