feat(pdf-generation): add custom MathJax CSS to PDF content

Integrates MathJax CSS directly into the PDF content to ensure consistent mathematical styling and formatting. This addresses visual discrepancies in PDF documents that include mathematical expressions.

functions.php

@@ -821,7 +821,12 @@ function handle_pdf_download()
                 $pdf->setTextColor(0);
                 $pdf->Ln(10);
                 $pdf->SetFont('helvetica', '', 12);
+
                 $content = apply_filters('the_content', $post->post_content);
+
+                $mathjax_css = file_get_contents(get_template_directory() . '/assets/dist/css/mathjax.css');
+                $content = "<style>$mathjax_css</style>$content";
+
                 $pdf->writeHTML($content);
 
                 // Output PDF document