Clarify comment: @mention highlight skips markdown-rendered elements

markdown.js already calls renderMarkdownElements() on DOMContentLoaded
for all [data-markdown] elements; ticket.js only processes plain-text
comments to avoid double-rendering.

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

assets/js/ticket.js

@@ -1181,7 +1181,7 @@ function highlightMentions(text) {
 document.addEventListener('DOMContentLoaded', function() {
     initMentionAutocomplete();
 
-    // Highlight existing mentions in comments
+    // Highlight @mentions in plain-text comments (markdown.js handles [data-markdown] elements)
     document.querySelectorAll('.comment-text').forEach(el => {
         if (!el.hasAttribute('data-markdown')) {
             el.innerHTML = highlightMentions(el.innerHTML);