Fix modal visibility using CSS class instead of HTML hidden attribute

Replace hidden attribute + [hidden] CSS selector with a .modal-open
class toggle. The hidden attribute approach was unreliable because
CSS display:flex was winning the specificity battle. Class-based
show/hide is explicit and not subject to attribute/cascade conflicts.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

admin/builder.php

@@ -184,7 +184,7 @@ $page_title = $session ? 'Edit: ' . htmlspecialchars($session['name']) : 'Rosary
 
 
 <!-- ── Create / Edit Prayer Modal ─────────────────────────────── -->
-<div id="prayer-modal" class="modal-overlay" hidden>
+<div id="prayer-modal" class="modal-overlay">
     <div class="modal-box">
         <h3 id="modal-title">New Custom Prayer</h3>