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.

server/__tests__/api.test.js

@@ -2040,6 +2040,16 @@ describe("Transcript cache integration", () => {
     assert.ok(heapLimit >= heapTotal && heapLimit > heapUsed);
   });
 
+  it("reports event-loop delay and the last hook / agents for the health score", async () => {
+    const res = await fetch("/api/settings/info");
+    const loop = res.body.server.event_loop;
+    for (const k of ["p50", "p99", "max"]) assert.ok(Number.isFinite(loop[k]), `event_loop.${k}`);
+    const a = res.body.activity;
+    assert.ok(a.last_event_at === null || typeof a.last_event_at === "string");
+    assert.ok(Number.isInteger(a.working_agents));
+    assert.ok(Number.isInteger(a.agents_24h.completed) && Number.isInteger(a.agents_24h.error));
+  });
+
   it("should evict cache entry on SessionEnd", async () => {
     const tmpTranscript = path.join(os.tmpdir(), `test-evict-${Date.now()}.jsonl`);
     fs.writeFileSync(