fix(hermes-agent): restrict /proc access in systemd services

Hermes strips sensitive env vars from tool subprocesses, but child
processes can recover them by reading /proc/<parent_pid>/environ. Add
ProtectProc=invisible and ProcSubset=pid to both systemd services to
hide other processes' /proc entries and limit /proc to the service's
own PID namespace.

Ref: https://github.com/NousResearch/hermes-agent/issues/4427

install/hermes-agent-install.sh

@@ -76,6 +76,8 @@ Environment="HERMES_HOME=/home/hermes/.hermes"
 Environment="HOME=/home/hermes"
 Restart=on-failure
 RestartSec=5
+ProtectProc=invisible
+ProcSubset=pid
 
 [Install]
 WantedBy=multi-user.target
@@ -103,6 +105,8 @@ Environment="PATH=/home/hermes/.local/bin:/usr/local/sbin:/usr/local/bin:/usr/sb
 Environment="NODE_OPTIONS=--max-old-space-size=3072"
 Restart=on-failure
 RestartSec=5
+ProtectProc=invisible
+ProcSubset=pid
 
 [Install]
 WantedBy=multi-user.target