style(web): denser trace waterfall aligned with the traces list - #2010

🟢 Confidence 10/10 · safe to merge. Presentational only, and every helper the new classes call was read: tone maps, getServiceColor's raw oklch() output, and the badge/eyebrow signatures all line up.
_{no findings · tests not needed · risk low}

Density pass on the trace waterfall: fixed 28px rows matching the virtualizer estimate, soft status badges shared with the traces list, per-service bar colours and eyebrow column labels. Presentational only; safe to merge.

• Waterfall rows pinned to h-7 and ROW_HEIGHT lowered 33 to 28
• Status cell renders traceStatusBadge / TONE_SOFT[severityTone()]
• Duration bars take the service colour through an inline background-color
• Leaf square flags only Error spans; header columns become eyebrows

_{92b329d · Reply "won't fix" to dismiss a finding, or mention @maple-review-bot to ask about one.}