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.js

@@ -247,6 +247,15 @@ function createOpenApiSpec() {
                 "The AI coding CLI that produced the session: `claude` (Claude Code's hooks and imported transcripts), `codex` (Codex's rollout journals and its opt-in hooks) `antigravity` (agy's conversation files and its opt-in hooks) or `cursor` (Cursor's agent transcripts — sessions only, no tokens).",
             },
             agent_count: { type: "integer", nullable: true },
+            owner_id: {
+              type: "integer",
+              nullable: true,
+              description:
+                "Server mode, list only: the account owning the session's workspace (its lane, else the lane of a dashboard run holding it); null when none. Absent in local mode.",
+            },
+            owner_name: { type: "string", nullable: true, description: "That owner's username." },
+            owner_display_name: { type: "string", nullable: true },
+            owner_avatar_at: { type: "string", format: "date-time", nullable: true },
             last_activity: { type: "string", format: "date-time", nullable: true },
             cost: { type: "number", nullable: true },
             awaiting_input_since: {
@@ -1234,6 +1243,32 @@ function createOpenApiSpec() {
                 node_version: { type: "string" },
                 platform: { type: "string" },
                 ws_connections: { type: "integer" },
+                event_loop: {
+                  type: "object",
+                  description:
+                    "Event-loop delay over the last minute in ms (p50, p99, max) — how long requests, hooks and terminal echo waited.",
+                  properties: {
+                    p50: { type: "number" },
+                    p99: { type: "number" },
+                    max: { type: "number" },
+                  },
+                },
+              },
+            },
+            activity: {
+              type: "object",
+              description:
+                "For the System Health score: when the newest event (hook) landed, agents working now, and how the agents that ended in the last 24 h ended (scoped to the caller's rows).",
+              properties: {
+                last_event_at: { type: "string", nullable: true },
+                working_agents: { type: "integer" },
+                agents_24h: {
+                  type: "object",
+                  properties: {
+                    completed: { type: "integer" },
+                    error: { type: "integer" },
+                  },
+                },
               },
             },
             transcript_cache: {