feat: add frontend search functionality with real-time results

- Create search.js with debounced input (300ms)
- Display results in dropdown modal with highlighted matches
- Support keyboard navigation (arrows, Enter, Escape)
- Show result count and 'no results' state
- Highlight matching terms in results
- Add autocomplete attribute to search input
- Minimum 2 characters to trigger search

templates/header.templ

@@ -19,6 +19,7 @@ templ Header(user User, currentPath string) {
                                placeholder="Search your library..." 
                                class="w-full px-4 py-2 pl-10 border rounded-lg" 
                                style="background-color: var(--bg-primary); color: var(--text-primary); border-color: var(--border);"
+                               autocomplete="off"
                         >
                         <svg class="absolute left-3 top-2.5 h-5 w-5" style="color: var(--text-secondary)" fill="none" stroke="currentColor" viewBox="0 0 24 24">
                             <path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M21 21l-6-6m2-5a7 7 0 11-14 0 7 7 0 0114 0z"/>