feat(bookmark): improve PDF bookmark extraction logic

enhance named destinations handling to support full name-tree traversal
add fallback page index resolution for better compatibility
fix parent-child relationship handling for zero-page bookmarks

src/pages/bookmark.html

@@ -293,7 +293,7 @@
             >
               <div class="flex flex-col items-center justify-center pt-4 pb-4">
                 <i
-                  data-lucide="file-text"
+                  data-lucide="sheet"
                   class="w-8 h-8 mb-2 text-gray-400"
                 ></i>
                 <p class="text-xs text-gray-400">