Thinking and Used tools are both auxiliary trace rows, but the thread list
was applying the same large gap used between full chat turns. That made
alternating Thinking / Used tools sequences look uneven and too airy.
Move row spacing from a fixed flex gap to per-row margins: full chat turns
keep mt-5, while consecutive auxiliary rows use mt-2. Add coverage for
Thinking -> Used tools -> Thinking spacing.
Co-authored-by: Cursor <cursoragent@cursor.com>
