docs: native Ubuntu install as primary; systemd and nginx

- install-ubuntu-24.04-native.md (production) and -docker.md (alternative)

- deploy/systemd/sac-api.service, nginx/sac.conf.example, env.native.example

- deployment, README, INDEX, work-plan, TZ updated

docs/work-plan.md

@@ -38,7 +38,7 @@
 | 1B.1 | Scaffold backend FastAPI | 🔄 |
 | 1B.2 | PostgreSQL + Alembic (hosts, events, api_keys) | 🔄 |
 | 1B.3 | `POST /api/v1/events`, `GET /health` | 🔄 |
-| 1B.4 | docker-compose + [install-ubuntu-24.04.md](install-ubuntu-24.04.md) | 🔄 |
+| 1B.4 | systemd + nginx + [install-ubuntu-24.04-native.md](install-ubuntu-24.04-native.md) | 🔄 |
 | 1B.5 | Валидация JSON Schema v1 | ⏳ |
 
 **Выход:** сервер Ubuntu принимает события от curl и от агентов в `dual`.