fix(traces): keep the sticky table header above the Trace ID links - #1195

🟢 Confidence 5/5 · safe to merge
_{quality 100/100 · no findings · tests not needed · risk low}

Raises the sticky traces table header from z-10 to z-20 so scrolled rows no longer paint over it. A one-class CSS fix, safe to merge.

_{5be79ee · Updated on every push. Reply "won't fix" to dismiss a finding, or mention @maple-review-bot to ask about one.}