feat: Reimplement PDF splitting functionality on a new dedicated page.

src/pages/merge-pdf.html

@@ -159,7 +159,7 @@
     <div class="bg-gray-800 rounded-lg shadow-xl p-6 max-w-sm w-full border border-gray-700">
       <h3 id="alert-title" class="text-xl font-bold text-white mb-2">Alert</h3>
       <p id="alert-message" class="text-gray-300 mb-6"></p>
-      <button id="alert-ok-btn" onclick="document.getElementById('alert-modal').classList.add('hidden')"
+      <button id="alert-ok"
         class="w-full bg-indigo-600 hover:bg-indigo-700 text-white font-semibold py-2 px-4 rounded-lg transition-colors duration-200">
         OK
       </button>