Refactor user detail page: split components, unify formatters

Break the 615-line UserDetail.tsx into focused sub-components
(header, stat cards, activity chart, request history, open alerts)
and extract shared utilities to lib/ (format, userChart,
enrichRequests). Promote storage load (GB/hr) to a stat card and
collapse the chart UX to a single metric picker. Add server-wide
average reference line alongside the user's own on every metric,
and link request titles to their Seerr pages.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/lib/format.ts

@@ -0,0 +1,27 @@
+export function formatGB(gb: number): string {
+  if (gb >= 1000) return `${(gb / 1000).toFixed(2)} TB`;
+  return `${gb.toFixed(1)} GB`;
+}
+
+export function formatHours(h: number): string {
+  if (h >= 1000) return `${(h / 1000).toFixed(1)}k h`;
+  return `${h.toFixed(0)}h`;
+}
+
+export function timeAgo(iso: string | null | undefined): string {
+  if (!iso) return "Never";
+  const diff = Date.now() - new Date(iso).getTime();
+  const mins = Math.floor(diff / 60_000);
+  if (mins < 1) return "just now";
+  if (mins < 60) return `${mins}m ago`;
+  const hrs = Math.floor(mins / 60);
+  if (hrs < 24) return `${hrs}h ago`;
+  const days = Math.floor(hrs / 24);
+  if (days < 30) return `${days}d ago`;
+  return new Date(iso).toLocaleDateString(undefined, { month: "short", year: "numeric" });
+}
+
+export function unixTimeAgo(ts: number | null): string {
+  if (ts === null) return "Never";
+  return timeAgo(new Date(ts * 1000).toISOString());
+}