feat(system): process heartbeat + /system/health, engine runs business fields (W9-I)

- process_heartbeat / process_heartbeat_sample (0034): api / worker / worker:agent / all
  upsert every 15s (event loop lag last/max, concurrency, running runs, SSE connections, memory)
- GET /system/health (admin): processes with 45s stale flag, SSE, DB latency/size/connections,
  disks (DATA_DIR / library roots / download dirs, cache thresholds), mount sentinel checks
  with IO timeout, engine pending/oldest/24h failure rate, schedules
- GET /system/health/history?hours=: bucketed lag / running / SSE series
- /engine/runs and /engine/runs/{id}: business {kind, refId, title, triggeredBy} joined from
  run input / task / agent_run / tasks_run_meta / outbox; businessKind / businessRefId filters
- docs/runbook/ops.md: field meanings and alert thresholds

Co-Authored-By: Claude Opus 5.5 <[email protected]>

apps/server/test/modules.test.ts

@@ -43,7 +43,7 @@ const pingModule: ServerModule = {
 };
 
 describe("ServerModule 骨架", () => {
-  it("清单里是四个 W2 模块 + 文件管理 + Pi 上游 + 定时任务 + 全局搜索(末尾),名字唯一", () => {
+  it("清单里是四个 W2 模块 + 文件管理 + Pi 上游 + 定时任务 + 全局搜索 + 进程与健康(末尾),名字唯一", () => {
     expect(SERVER_MODULES.map((m) => m.name)).toEqual([
       "auth-settings",
       "sources-identity",
@@ -53,6 +53,7 @@ describe("ServerModule 骨架", () => {
       "pi",
       "schedules",
       "search",
+      "system",
     ]);
   });