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/components/RankChip.tsx

@@ -0,0 +1,15 @@
+export default function RankChip({
+  rank,
+  total,
+}: {
+  rank: number | null;
+  total: number;
+}) {
+  if (rank === null) return <span className="text-slate-700">—</span>;
+  return (
+    <span className="text-xs font-mono text-slate-500">
+      #{rank}
+      <span className="text-slate-700">/{total}</span>
+    </span>
+  );
+}