feat(template): Display author/date in muted text style

Wrapped author name and date in a <p> tag with a muted text class
to enhance readability and visual hierarchy on the 'single-letter'
template. Additionally, added missing newline after 'register_post_type'
call in functions.php for better code formatting.

Addresses visual consistency and readability issues.

functions.php

@@ -455,6 +455,7 @@ function create_letter_post_type() {
 
     register_post_type('letter', $args);
 }
+
 add_action('init', 'create_letter_post_type');
 
 function add_letter_meta_boxes() {

single-letter.php

@@ -6,6 +6,7 @@
         <div class="col-lg-8 mx-auto">
             <?php if (have_posts()) : while (have_posts()) : the_post(); ?>
                     <h1 class="display-4"><?php the_title(); ?></h1>
+                    <p class="text-muted">
                         <?php
                         $authors = get_post_meta(get_the_ID(), 'article_authors', true);
                         if (!empty($authors)) {
@@ -14,6 +15,7 @@
                             the_author();
                         }
                         ?> | <?php the_date(); ?>
+                    </p>
                     <?php if (has_post_thumbnail()) : ?>
                         <img src="<?php the_post_thumbnail_url(); ?>" class="img-fluid mb-4" alt="<?php the_title(); ?>">
                     <?php endif; ?>