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

deploy/systemd/sac-api.service

@@ -0,0 +1,21 @@
+[Unit]
+Description=Security Alert Center API (FastAPI)
+Documentation=https://git.kalinamall.ru/PapaTramp/security-alert-center
+After=network-online.target postgresql.service
+Wants=network-online.target
+Requires=postgresql.service
+
+[Service]
+Type=simple
+User=sac
+Group=sac
+WorkingDirectory=/opt/security-alert-center/backend
+EnvironmentFile=/etc/security-alert-center/sac-api.env
+Environment=PYTHONPATH=/opt/security-alert-center/backend
+ExecStart=/opt/security-alert-center/backend/.venv/bin/uvicorn app.main:app --host 127.0.0.1 --port 8000
+Restart=on-failure
+RestartSec=5
+NoNewPrivileges=true
+
+[Install]
+WantedBy=multi-user.target