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__/server-mode-rows.test.js

@@ -209,6 +209,12 @@ describe("server mode: list and aggregate routes", () => {
     }
   });
 
+  it("names each listed session's owner: a stamped lane, else a run's lane", async () => {
+    const { sessions } = await get("/api/sessions", "boss");
+    const owners = Object.fromEntries(sessions.map((s) => [s.id, s.owner_name]));
+    assert.deepEqual(owners, { sA: "alice", sA2: "alice", sB: "bob", sHost: null });
+  });
+
   it("keeps a member out of another's rows through filters and POST", async () => {
     // A filter naming another's session is refused, not answered empty.
     assert.equal((await call("GET", "/api/events?session_id=sB", { as: "alice" })).status, 404);