feat: restore bookshelf page route and add navigation link

- Add /bookshelf route in frontend.go (was typo /booskshelf)
- Route fetches libraries server-side and renders complete HTML
- Supports library_id query param or defaults to user's first library
- Add "All Books" link to header navigation
- Follows SSR-first architecture principles

Fixes route registration that prevented bookshelf page from loading.

templates/header.templ

@@ -14,6 +14,13 @@ templ Header(user User, currentPath string) {
 						<a href="/dashboard" class="text-sm hover:opacity-80 transition-opacity" style="color: var(--text-secondary); text-decoration: none;">
 							Library
 						</a>
+						<a
+							href="/bookshelf"
+							class="text-sm hover:opacity-80 transition-opacity"
+							style="color: var(--text-secondary); text-decoration: none;"
+						>
+							All Books
+						</a>
 						<a href="/collections" class="text-sm hover:opacity-80 transition-opacity" style="color: var(--text-secondary); text-decoration: none;">
 							Collections
 						</a>