Add modal-title placeholder for W3C validation

The aria-labelledby needs a static element in HTML since the validator
doesn't execute JavaScript. Added placeholder h2 that gets replaced
when modal opens.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/index.html b/index.html
index e341be1..b1b8d7c 100644
--- a/index.html
+++ b/index.html
@@ -49,7 +49,7 @@
   <!-- Modal for book details -->
   <div class="modal-overlay" id="book-modal" role="dialog" aria-modal="true" aria-labelledby="modal-title">
     <div class="modal-content" id="modal-content">
-      <!-- Modal content populated by JavaScript -->
+      <h2 id="modal-title" class="visually-hidden">Book Details</h2>
     </div>
   </div>