feat: workerize external generation

deploy/systemd/genarrative-external-generation-worker@.service

@@ -0,0 +1,29 @@
+[Unit]
+Description=Genarrative External Generation Worker %i
+After=network-online.target spacetimedb.service
+Wants=network-online.target
+Requires=spacetimedb.service
+
+[Service]
+Type=simple
+User=genarrative
+Group=genarrative
+WorkingDirectory=/opt/genarrative/current
+EnvironmentFile=/etc/genarrative/api-server.env
+EnvironmentFile=-/etc/genarrative/external-generation-worker.env
+ExecStart=/usr/bin/env GENARRATIVE_PROCESS_ROLE=external-generation-worker GENARRATIVE_EXTERNAL_GENERATION_WORKER_ID=%H-%i GENARRATIVE_TRACKING_OUTBOX_DIR=/var/lib/genarrative/tracking-outbox/%H-%i OTEL_SERVICE_NAME=genarrative-external-generation-worker /opt/genarrative/current/api-server
+Restart=always
+RestartSec=5
+KillSignal=SIGINT
+TimeoutStopSec=7200
+LimitNOFILE=65535
+TasksMax=2048
+
+# worker 复用 api-server 发布目录；外部生成审计与临时运行态只写服务端私有目录。
+NoNewPrivileges=true
+PrivateTmp=true
+ProtectSystem=full
+ReadWritePaths=/opt/genarrative /var/lib/genarrative
+
+[Install]
+WantedBy=multi-user.target