fix(system): retired heartbeat rows no longer alarm on status page

- GET /system/health splits processes into current instances (hosts with
  a beat in the last 10 min, newest per host+kind, not stopped) and
  retiredProcesses[]; 45s stale and level only consider current ones
- heartbeat writer marks stopped_at on graceful exit (migration 0043),
  upsert clears it; pure api role now stops its writer on SIGTERM
- scheduled job system.heartbeat_cleanup (maintain, 1h) deletes rows
  without a beat for 24h and samples older than 7 days
- status page: per-role alarms ("io worker 45 秒没有心跳"), collapsible
  retired instances; glossary/runbook updated
- bump all members to 0.2.2, CHANGELOG [0.2.2]

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

packages/tasks/deno.json

@@ -1,6 +1,6 @@
 {
   "name": "@umt/tasks",
-  "version": "0.2.0",
+  "version": "0.2.2",
   "exports": { ".": "./src/index.ts" },
   "tasks": {
     "test": "deno run -A npm:vitest run",