Dashboard — UX batch

Motivation

Continuation of the UI/UX pass on the Dashboard / Monitor surface. Most candidates were already implemented in this mature area, so this batch lands only the two genuine gaps and leaves the rest untouched.

Verified-already-present (left untouched): unified card skeletons (RowSkeleton + .skeleton, tokens just fixed 2026-06-21), shared degraded tone (DegradedNotice), "n ago" labels (useRelativeTime), cluster status AA colors (.gt-*), empty jobs CTA (JobsEmptyState), responsive single- column grid (.dashboard-grid @768px). Deferred (need a shared refresh clock or per-card refetch wiring + visual verification): RefreshRing countdown integration (#33) and a retry action on DegradedNotice cards (#40).

User-facing change

• #37 Toast stack cap — at most four toasts now stack at once; a rapid-fire burst (e.g. a failing poll retrying) drops the oldest overflow immediately instead of burying the screen.
• #39 .tabular-nums utility — a shared class for the existing ad-hoc font-variant-numeric: tabular-nums convention, so future numeric columns align without re-declaring the inline style.

Code change summary

• web/src/components/Toast.tsx: MAX_TOASTS = 4; the toast() reducer slices to the most recent four.
• web/src/theme/glass.css: .tabular-nums utility class.

Validation evidence

• cd web && npm run build → clean.
• npx eslint src/components/Toast.tsx → clean.

No backend / API / IaC changes.