feat(activity-log): phase 2 - recorder, actor context, retention, lifecycle

- ActivityRecorder: thread-safe record() (inline on loop, call_soon_threadsafe off-loop), best-effort, fires activity_logged event
- current_actor ContextVar set in verify_api_key (both branches), default system
- ActivityLogRetentionEngine: prune loop (max_days+max_entries), settings persistence, rehydrates recorder.enabled on startup
- lifespan wiring: server.shutting_down recorded first on shutdown, retention stop before db.close
- events-ws.ts allowlist + parity; DI getters + module accessor; 62 new tests

plans/activity-log/PLAN.md

@@ -80,7 +80,7 @@ is an on-demand CSV/JSON **export** (no separate backup subsystem).
 | Phase | Domain | Status | Review | Build | Committed |
 |-------|--------|--------|--------|-------|-----------|
 | Phase 1: Storage | data | ✅ Done | ✅ Passed | ✅ Passed | ✅ |
-| Phase 2: Recorder/Retention | backend | ⬜ Not Started | ⬜ | ⬜ | ⬜ |
+| Phase 2: Recorder/Retention | backend | ✅ Done | ✅ Passed | ✅ Passed | ✅ |
 | Phase 3: Instrumentation | backend | ⬜ Not Started | ⬜ | ⬜ | ⬜ |
 | Phase 4: REST API | backend | ⬜ Not Started | ⬜ | ⬜ | ⬜ |
 | Phase 5: Frontend tab | frontend | ⬜ Not Started | ⬜ | ⬜ | ⬜ |