feat(health): System Health in three groups, a score that sees lag; admin user detail

Dashboard → System Health is grouped into AgentHub, Machine and Agent
activity. The machine (GET /api/host, every signed-in user) is drawn by
components/health/HostHealth.tsx: host card beside the CPU/memory history,
then CPU (threads as compact cells + temperatures/GPUs), disks & network,
busiest processes, and per-user tiles. Concurrency bars each show their own
agent type on hover.

The Health Score (client/src/lib/healthScore.ts) is now 100 minus what each
check costs, between an amber and a red threshold: event-loop p99
(server/lib/loop-delay.js, shared with /api/metrics), Linux PSI pressure for
CPU, memory and disk I/O (/api/host `pressure`; load per core without PSI),
RAM, the database's disk, V8 heap, hooks silent while agents work, and agent
errors in the last 24 h. All-time success rate, API errors and the transcript
cache hit rate no longer count. /api/settings/info adds server.event_loop and
activity {last_event_at, working_agents, agents_24h}.

Administration: a user row opens its detail in place (GET
/api/users/:id/details — spend, account pool share, live panes, workspaces,
newest sessions); the server panel is gone, member tmux folded into the table;
the Sessions list shows each row's owner in server mode.

client/src/components/users/AccountPoolCard.tsx

@@ -72,15 +72,15 @@ type Row = {
 };
 
 /** One quota window of an account: % used and when it rolls over. */
-type QuotaWindow = { key: "5h" | "wk"; used: number | null; resetsAt: string | null };
+export type QuotaWindow = { key: "5h" | "wk"; used: number | null; resetsAt: string | null };
 
 /**
  * The 5-hour and weekly windows of an account, from Claude's `fiveHour` /
  * `sevenDay` or Codex's `5h` / `wk` rollout windows. A window whose reset has
  * passed is empty again (the reading predates it), as the balancer treats it.
  */
-function windowsOf(
-  a: AccountPool["accounts"][number] | AccountPool["codex"][number]
+export function windowsOf(
+  a: Pick<AccountPool["accounts"][number] | AccountPool["codex"][number], "quota">
 ): QuotaWindow[] {
   const q = a.quota as
     | {
@@ -558,7 +558,7 @@ function AccountCard({
  * One window of an account's quota, shown as what is LEFT (100% = untouched,
  * 0% = used up), with when it resets.
  */
-function QuotaBar({ window: w }: { window: QuotaWindow }) {
+export function QuotaBar({ window: w }: { window: QuotaWindow }) {
   const { t } = useTranslation("users");
   const left = w.used == null ? null : Math.max(0, Math.min(100, 100 - Math.round(w.used)));
   const resets = untilText(w.resetsAt);