fix: account for sticky file header in comment navigation scroll (#67)

When navigating between comments with [ ] in multi-file or git mode,
the scroll offset only subtracted the main app header height, leaving
the top of the comment card hidden behind the sticky file header.

Now also measures the target comment's .file-header height and adds
it to the scroll offset.

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: tomasz-tomczyk

assets/js/document-renderer.js

@@ -3451,7 +3451,10 @@ function navigateToComment(ctx, direction) {
   ctx._navCommentId = target.dataset.commentId
 
   const rect = target.getBoundingClientRect()
-  window.scrollTo({ top: rect.top + window.scrollY - headerHeight - 16, behavior: 'smooth' })
+  const fileSection = target.closest('.file-section')
+  const fileHeader = fileSection ? fileSection.querySelector('.file-header') : null
+  const fileHeaderHeight = fileHeader ? fileHeader.offsetHeight : 0
+  window.scrollTo({ top: rect.top + window.scrollY - headerHeight - fileHeaderHeight - 16, behavior: 'smooth' })
   target.classList.add('comment-nav-highlight')
   setTimeout(() => target.classList.remove('comment-nav-highlight'), 1000)
 }