Separate commit details from changed files

TESTING.md

@@ -230,11 +230,12 @@ xcrun simctl launch booted de.rfc1437.gotcha
       branch whose tip was deleted.
 - [ ] Open a commit and verify its header shows the full title and description,
       full hash, author, committer, date, known branch/ref, and signature status
-      above the Changed Files paths and statuses. Unsigned commits say
-      **Unsigned**. Verify paragraphs, lists, links, and inline styles in a
-      multi-line commit description use the repository file Preview Markdown
-      presentation. Check that long values wrap and remain readable at the
-      largest Dynamic Type accessibility size.
+      above the Changed Files paths and statuses, with a thin system separator
+      between the header and first file. Unsigned commits say **Unsigned**.
+      Verify paragraphs, lists, links, and inline styles in a multi-line commit
+      description use the repository file Preview Markdown presentation. Check
+      that long values wrap and remain readable at the largest Dynamic Type
+      accessibility size.
 - [ ] Open a changed file and verify the diff title, old/new line numbers,
       monospaced text, addition/removal/hunk colors, vertical scrolling, and
       source-style horizontal scrolling for long lines without word wrapping,