feat(manager): add remote VM support via NEXUS_SERVER_HOST

- config.py: add NEXUS_SERVER_HOST env var for cross-VM deployment
- health_service.py: graceful Redis failure when only localhost-bound
- systemd service: document remote VM configuration
- README: add dedicated 'VM separada' installation section
- .env.example: new file with remote connection examples

manager/systemd/nexus-manager.service

@@ -1,6 +1,6 @@
 [Unit]
 Description=Nexus Instance Manager (Control Central)
-After=network.target postgresql.service
+After=network.target
 
 [Service]
 Type=simple
@@ -9,13 +9,28 @@ WorkingDirectory=/home/Autopartes/manager
 ExecStart=/usr/local/bin/gunicorn -w 2 --threads 4 -b 0.0.0.0:5003 "app:create_app()"
 Restart=always
 RestartSec=5
+
+# ─── Local Paths ───────────────────────────────────────────────────────────
 Environment=PYTHONUNBUFFERED=1
 Environment=PYTHONPATH=/home/Autopartes/manager:/home/Autopartes/pos
+Environment=POS_DIR=/home/Autopartes/pos
+
+# ─── Database (UPDATE FOR REMOTE VM) ───────────────────────────────────────
+# If manager runs on a separate VM, change localhost to the IP of the
+# PostgreSQL server (e.g. 192.168.10.91).
 Environment=MASTER_DB_URL=postgresql://postgres@localhost/nexus_autoparts
 Environment=TENANT_DB_URL_TEMPLATE=postgresql://postgres@localhost/{db_name}
+
+# ─── Remote Nexus Server IP ────────────────────────────────────────────────
+# Set to the IP/hostname of the server running POS/Dashboard/Quart/Redis.
+# Leave as 127.0.0.1 if manager runs on the same server.
+Environment=NEXUS_SERVER_HOST=127.0.0.1
+
+# ─── Security (CHANGE THIS) ────────────────────────────────────────────────
 Environment=MANAGER_JWT_SECRET=change-me-to-a-random-64-char-hex-string
-Environment=POS_DIR=/home/Autopartes/pos
-Environment=REDIS_URL=redis://localhost:6379/0
+
+# ─── Redis (optional, health check only) ───────────────────────────────────
+Environment=REDIS_URL=redis://127.0.0.1:6379/0
 
 [Install]
 WantedBy=multi-user.target