activity: follow the agent's background work live + chat-event retention

"Activity" (placeholder name — jobs/tasks were taken) = watch background tasks
scroll in parallel with chat. Built DB-free; NOT restarted — deploy + test in
the morning.

- NDJSON progress contract (activity/progress.ts): capabilities append
  {job,cap,phase,status,pct,detail,ts,...} lines; tolerant parser treats any
  JSON object with phase/status as structured progress, else a raw log line.
- Backend (activity/router.ts, owner-only, path-guarded):
  - GET /api/activity/tasks — registry by scanning /tmp/claude-*/<cwd>/tasks/
    *.output (harness run_in_background) + announced detached jobs.
  - POST /api/activity/announce {name,path} — register a detached (setsid) job's
    log so it's followable too (the setsid case is on the critical path, since
    the warm worker now makes plain run_in_background the default for heavy jobs).
  - GET /api/activity/stream?task=<id>|path=<abs> — SSE tail (poll + offset),
    emitting {kind:'line'|'progress'} with NDJSON parsed.
- Frontend /activity screen + Radio nav item: task list (active dot) → live tail
  with a phase/pct progress header + raw log, following the /system-monitor pattern.
- Retention: startChatEventRetention() prunes chat_session_events >7d every 6h
  (wired in bootstrap) so the durable queue stays bounded.

Verified headlessly (no restart): parseTailLine classification, and the scan
finds 53 real task output files. Endpoints + UI untested until deploy.

Deferred (see handoff): cross-device sync + OpenCode parity (both touch the
now-stable chat path — won't ship un-restart-tested); task:progress into chat.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/servers/hono.ts

@@ -21,6 +21,7 @@ import { taskLogsRouter } from './api/task-logs/task-logs';
 import { router as fileBrowserRouter } from './api/file-browser/router';
 import { musicRouter } from './api/music/router';
 import { systemMonitorRouter } from './api/system-monitor/system-monitor';
+import { activityRouter } from './api/activity/router';
 import './api/music/sidecar-server'; // side-effect: capture the officer-music audio server port
 import { devServerRouter, devServerProxyRouter } from './api/dev-server/router';
 import { dockRouter } from './api/dock/dock';
@@ -95,6 +96,7 @@ protectedRouter.route('/task-logs', taskLogsRouter);
 protectedRouter.route('/file-browser', fileBrowserRouter);
 protectedRouter.route('/music', musicRouter);
 protectedRouter.route('/system-monitor', systemMonitorRouter);
+protectedRouter.route('/activity', activityRouter);
 protectedRouter.route('/dev-server', devServerRouter);
 protectedRouter.route('/dock', dockRouter);
 protectedRouter.route('/integrations', integrationsRouter);