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/openapi-extra/artifacts.js

@@ -1,6 +1,6 @@
 /**
  * @file OpenAPI fragment for the Artifacts hub (`/api/artifacts/*`, server/routes/artifacts.js)
- * and the Administration page's Server tab (`GET /api/host`, server/routes/host.js).
+ * and the Dashboard System Health tab's machine cards (`GET /api/host` and `/api/host/history`, server/routes/host.js).
  * Hand-written from the routes; docs/API.md § Artifacts hub is the long form.
  * @author Nguyễn Ngọc Trí Vĩ <vinnt@smartgift.vn>
  */
@@ -14,7 +14,7 @@ const tags = [
   {
     name: "Host",
     description:
-      "Administration → Server: the machine's hardware, load, disks and each user's share of CPU and memory. Read-only, staff only in server mode.",
+      "Dashboard → System Health: the machine's hardware, load, disks and each user's share of CPU and memory. Read-only, every signed-in user.",
   },
 ];
 
@@ -385,13 +385,36 @@ const paths = {
       responses: {
         200: {
           description:
-            "`{at, hostname, os, uptime, cpu, memory, disks, homesMount, gpus, usage}` — see docs/API.md.",
+            "`{at, hostname, os, uptime, bootTime, cpu (+physicalCores, perCore), memory, disks, homesMount, gpus, usage, network, diskIo, temperatures, pressure, topProcesses, process}` — see docs/API.md.",
           content: { "application/json": { schema: { type: "object" } } },
         },
         500: { description: "EHOST" },
       },
     },
   },
+  "/api/host/history": {
+    get: {
+      tags: ["Host"],
+      summary: "The machine's CPU/memory history since the server started",
+      operationId: "getHostHistory",
+      description:
+        "In memory only: one point every 30 s for 24 h, kept by a server-mode server on Linux (empty otherwise, `running: false`). Averaged down to at most 360 points. Server mode: admin/analyst only.",
+      parameters: [
+        {
+          name: "range",
+          in: "query",
+          schema: { type: "string", enum: ["1h", "6h", "24h"], default: "1h" },
+        },
+      ],
+      responses: {
+        200: {
+          description:
+            "`{range, intervalMs, running, startedAt, points: [{at, cpu, memory, memoryUsed, swapUsed, load1, users: {<userId>: {cpu, memory}}}]}`.",
+          content: { "application/json": { schema: { type: "object" } } },
+        },
+      },
+    },
+  },
 };
 
 module.exports = { tags, schemas, paths };