fix: prevent systemd restart storm on gateway connection failure

Cherry-picked from PR #2319 by @itenev.

When the gateway fails to connect (e.g. PrivilegedIntentsRequired,
missing token), systemd's default RestartSec=10 with no start rate
limit causes rapid reconnect storms flooding logs and triggering
platform-side rate limits.

- StartLimitIntervalSec=600 + StartLimitBurst=5 in [Unit] (max 5
  restarts per 10 min)
- RestartSec: 10 → 30
- Applied to both templates in gateway.py and scripts/hermes-gateway

scripts/hermes-gateway

@@ -82,13 +82,15 @@ def generate_systemd_unit() -> str:
     return f"""[Unit]
 Description={SERVICE_DESCRIPTION}
 After=network.target
+StartLimitIntervalSec=600
+StartLimitBurst=5
 
 [Service]
 Type=simple
 ExecStart={python_path} {script_path} run
 WorkingDirectory={working_dir}
 Restart=on-failure
-RestartSec=10
+RestartSec=30
 StandardOutput=journal
 StandardError=journal