Fix the width of the discussion header.
Review Request #15010 — Created April 8, 2026 and updated — Latest diff uploaded
The new discussion header component was using its natural width, which
in real-world usage doesn't allow the timestamp to stay aligned to the
right of the review box. This is a simple fix that assigns a 100% width
to the header.
Tested on desktop and mobile with reviews and replies. Verified that the
layout had full width and displayed as expected in all cases.