docs: clarify gateway service scopes (#1378)

website/docs/guides/daily-briefing-bot.md

@@ -29,7 +29,8 @@ Before starting, make sure you have:
 - **Hermes Agent installed** — see the [Installation guide](/docs/getting-started/installation)
 - **Gateway running** — the gateway daemon handles cron execution:
   ```bash
-  hermes gateway install   # Install as system service (recommended)
+  hermes gateway install   # Install as a user service
+  sudo hermes gateway install --system   # Linux servers: boot-time system service
   # or
   hermes gateway           # Run in foreground
   ```
@@ -242,10 +243,12 @@ Make sure the scheduler is actually running:
 hermes cron status
 ```
 
-If the gateway isn't running, your jobs won't execute. Install it as a system service for reliability:
+If the gateway isn't running, your jobs won't execute. Install it as a background service for reliability:
 
 ```bash
 hermes gateway install
+# or on Linux servers
+sudo hermes gateway install --system
 ```
 
 ## Going Further

website/docs/guides/team-telegram-assistant.md

@@ -143,12 +143,13 @@ For a persistent deployment that survives reboots:
 
 ```bash
 hermes gateway install
+sudo hermes gateway install --system   # Linux only: boot-time system service
 ```
 
-This creates a **systemd** service (Linux) or **launchd** service (macOS) that runs automatically.
+This creates a background service: a user-level **systemd** service on Linux by default, a **launchd** service on macOS, or a boot-time Linux system service if you pass `--system`.
 
 ```bash
-# Linux — manage the service
+# Linux — manage the default user service
 hermes gateway start
 hermes gateway stop
 hermes gateway status
@@ -158,6 +159,11 @@ journalctl --user -u hermes-gateway -f
 
 # Keep running after SSH logout
 sudo loginctl enable-linger $USER
+
+# Linux servers — explicit system-service commands
+sudo hermes gateway start --system
+sudo hermes gateway status --system
+journalctl -u hermes-gateway -f
 ```
 
 ```bash