fix(forgejo-runner): cd to /root before runner registration

forgejo-runner register writes .runner config to the current working
directory. The install script runs in a temp directory (via build.func),
so the config was lost on cleanup. The systemd service expects it in
/root (WorkingDirectory=/root), so cd there before registering.

install/forgejo-runner-install.sh

@@ -60,6 +60,7 @@ msg_ok "Installed Forgejo Runner"
 
 msg_info "Registering Forgejo Runner"
 export DOCKER_HOST="unix:///run/podman/podman.sock"
+cd /root
 forgejo-runner register \
   --instance "$FORGEJO_INSTANCE" \
   --token "$FORGEJO_RUNNER_TOKEN" \