feat(hermesagent): replace shim+system-unit pattern with hermes-native user services

The previous approach used a /usr/bin/hermes shim to proxy commands from root
to the hermes user, and a hand-crafted system-level systemd unit for the
gateway. This worked for the default profile but broke down for named profiles:

- hermes profile create <name> generates an alias script in
  ~/.local/bin/<name> that calls hermes with -p <name>. These aliases live
  in the hermes user's PATH, not root's, so root could not invoke them.
- Maintaining parity would require per-profile shims, a watcher daemon to
  create/remove them, and system-unit mirrors for each profile gateway — all
  of which would need to stay in sync with hermes internals across updates.

New approach — work with hermes, not around it:

- loginctl enable-linger hermes: ensures the hermes user's systemd session
  starts at boot and persists without login. All user-unit gateways (default
  and per-profile) now survive reboots automatically.
- Gateway service management delegated entirely to hermes: 'hermes gateway
  install' / 'hermes setup' create and enable the user unit natively.
  The install script no longer pre-installs the gateway; hermes prompts the
  user to do so at the end of 'hermes setup'.
- hermes-dashboard.service remains a system unit (no native install command
  exists for it). Its After= no longer references hermes-gateway.service
  since there is no system-unit gateway to depend on.
- /usr/bin/hermes shim removed. Root is guided to 'su - hermes' via a two-
  line /etc/profile.d/hermes-hint.sh message on login, with a one-liner to
  make the switch automatic. Once logged in as hermes, all hermes commands,
  profile aliases, and gateway management work natively.
- update_script simplified: only hermes-dashboard (our unit) is stopped and
  restarted. hermes update --yes handles gateway service lifecycle itself.

ct/hermesagent.sh

@@ -31,7 +31,6 @@ function update_script() {
 
   msg_info "Stopping Services"
   systemctl stop hermes-dashboard
-  systemctl stop hermes-gateway
   msg_ok "Stopped Services"
 
   msg_info "Updating ${APP}"
@@ -43,7 +42,6 @@ function update_script() {
   msg_ok "Updated ${APP}"
 
   msg_info "Starting Services"
-  systemctl start hermes-gateway
   systemctl start hermes-dashboard
   msg_ok "Started Services"
   msg_ok "Updated successfully!"
@@ -58,6 +56,7 @@ msg_ok "Completed successfully!\n"
 echo -e "${CREATING}${GN}${APP} setup has been successfully initialized!${CL}"
 echo -e "${INFO}${YW} Connect via SSH and configure your LLM provider:${CL}"
 echo -e "${TAB}${GATEWAY}${BGN}ssh root@${IP}${CL}"
+echo -e "${TAB}${BGN}su - hermes${CL}"
 echo -e "${TAB}${BGN}hermes setup${CL}"
 echo -e "${INFO}${YW} API Server (OpenAI-compatible):${CL}"
 echo -e "${TAB}${GATEWAY}${BGN}http://${IP}:8642/v1${CL}"