feat(admin): Administration page — Users tab + Server tab (hardware, per-user CPU/memory/home share)

/users becomes /admin (redirected), a tab shell over the existing Users view
and a new Server tab backed by GET /api/host (server/lib/host-stats.js):
hostname/OS/uptime, CPU and load, memory and swap, every real disk with
HDD/SSD, NVIDIA GPUs, and each user's live share from two /proc samples —
attributed by the member's Linux uid (S3) or, for host processes, by the
inherited AGENTHUB_LANE_ID's workspace owner. Read-only, staff-only (/host
in STAFF_ONLY_PREFIXES), comm names only. Members' tmux card moves to the
Server tab.

server/__tests__/host-stats.test.js

@@ -0,0 +1,70 @@
+/**
+ * @file host-stats.test.js
+ * @description Tests for server/lib/host-stats.js — the Server tab's hardware
+ * snapshot and per-user CPU/memory attribution (`GET /api/host`).
+ * @author Nguyễn Ngọc Trí Vĩ <vinnt@smartgift.vn>
+ */
+
+const { test } = require("node:test");
+const assert = require("node:assert/strict");
+const { hostStats, mountOf, __setDeps } = require("../lib/host-stats");
+
+const linux = process.platform === "linux";
+
+test("mountOf picks the longest mount point holding the path", () => {
+  const list = [{ mount: "/" }, { mount: "/srv" }, { mount: "/srv/users" }];
+  assert.equal(mountOf(list, "/srv/users/alice"), "/srv/users");
+  assert.equal(mountOf(list, "/srv/usersx"), "/srv");
+  assert.equal(mountOf(list, "/home/x"), "/");
+  assert.equal(mountOf(list, null), null);
+});
+
+test("hostStats reports hardware and attributes processes by uid", { skip: !linux }, async () => {
+  const me = process.getuid();
+  __setDeps({
+    users: () => [
+      { id: 7, username: "zed" },
+      { id: 8, username: "idle" },
+    ],
+    memberNameForUid: (uid) => (uid === me ? "zed" : null),
+    laneOwner: () => null,
+    homesRoot: () => "/",
+    wait: () => new Promise((r) => setTimeout(r, 20)),
+  });
+  const r = await hostStats();
+  assert.ok(r.cpu.cores > 0);
+  assert.ok(r.memory.total > 0 && r.memory.used >= 0);
+  assert.ok(Array.isArray(r.disks));
+  const zed = r.usage.groups.find((g) => g.key === "user:7");
+  assert.ok(zed.processes > 0, "this test's own process belongs to zed");
+  assert.ok(zed.memory > 0);
+  assert.ok(zed.top.every((t) => typeof t.name === "string" && !("argv" in t)));
+  const idle = r.usage.groups.find((g) => g.key === "user:8");
+  assert.deepEqual([idle.cpu, idle.memory, idle.processes], [0, 0, 0]);
+  assert.equal(
+    r.usage.groups.find((g) => g.key === "host"),
+    undefined
+  );
+});
+
+test(
+  "a host process with a workspace's AGENTHUB_LANE_ID counts for its owner",
+  { skip: !linux },
+  async () => {
+    const { spawn } = require("node:child_process");
+    const child = spawn("sleep", ["5"], { env: { ...process.env, AGENTHUB_LANE_ID: "4242" } });
+    try {
+      __setDeps({
+        users: () => [{ id: 3, username: "own" }],
+        memberNameForUid: () => null,
+        laneOwner: (id) => (id === 4242 ? 3 : null),
+        wait: () => new Promise((r) => setTimeout(r, 20)),
+      });
+      const r = await hostStats();
+      const own = r.usage.groups.find((g) => g.key === "user:3");
+      assert.ok(own.top.some((t) => t.pid === child.pid));
+    } finally {
+      child.kill();
+    }
+  }
+);