Debounce the live markdown preview (#108)

updatePreview() was bound directly to the comment textarea's 'input'
event with no debounce, re-running the full markdown parser (regex
passes for headings, tables, links, footnotes, etc.) on every single
keystroke.

Wrapped it with the existing lt.debounce() helper (150ms) — the
initial preview render on enabling the toggle still happens
immediately; only the per-keystroke live updates are debounced.
Verified via jsdom with real timers: 10 rapid keystrokes within the
debounce window produce exactly one parse call instead of ten.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Lhz7pGMaoTfL5sdYS5XiKv

assets/js/ticket.js

@@ -357,12 +357,17 @@ function togglePreview() {
 
     if (isPreviewEnabled) {
         preview.innerHTML = parseMarkdown(textarea.value);
-        textarea.addEventListener('input', updatePreview);
+        textarea.addEventListener('input', debouncedUpdatePreview);
     } else {
-        textarea.removeEventListener('input', updatePreview);
+        textarea.removeEventListener('input', debouncedUpdatePreview);
     }
 }
 
+// Re-running the full markdown parser on every single keystroke is wasted
+// work while the user is still mid-word; 150ms debounce keeps the preview
+// feeling live without re-parsing on every keystroke.
+const debouncedUpdatePreview = window.lt ? lt.debounce(updatePreview, 150) : updatePreview;
+
 function updatePreview() {
     const textarea = document.getElementById('newComment');
     const previewDiv = document.getElementById('markdownPreview');