admin: fix dashboard phantom scroll, drop last-failure column from upstream table

the chart's screen-reader table wore srOnly directly; overflow and
height do not apply to a table box, so it laid out 1200px tall below
the page while clip-path hid the paint. wrap it in a hidden div, which
clips properly and keeps the table role. failure detail is the
diagnostics page's job since milestone 27; the column and the now
dead formatAge go.

admin/src/lib/format.ts

@@ -28,21 +28,9 @@ const AGE_UNITS = [
 ] as const;
 
 /**
- * Seconds of elapsed time → a coarse "3h ago". Truncating and single-unit on
- * purpose: this labels a snapshot the caller renders once, so a reader must not
- * take it for a live count. Nothing re-renders it as it ages.
- */
-export function formatAge(seconds: number): string {
-	for (const unit of AGE_UNITS) {
-		if (seconds >= unit.seconds) return `${Math.floor(seconds / unit.seconds)}${unit.suffix} ago`;
-	}
-	return `${Math.floor(seconds)}s ago`;
-}
-
-/**
- * Seconds of elapsed time → a coarse "3h", the same single truncated unit as
- * `formatAge` without the "ago". For a span the caller labels itself, as in
- * "active for 3h". A negative span reads "0s": clock skew is not a duration.
+ * Seconds of elapsed time → a coarse "3h". Truncating and single-unit on
+ * purpose, for a span the caller labels itself, as in "active for 3h". A
+ * negative span reads "0s": clock skew is not a duration.
  */
 export function formatDuration(seconds: number): string {
 	for (const unit of AGE_UNITS) {