jmri: add rblundon@laptop SSH key for xpra access

Adds jmri_ssh_authorized_keys_extra list to support multiple authorized
keys on the jmri account. Deploys rblundon's MacBook key so xpra can
connect via SSH without a password.

ansible/roles/jmri/defaults/main.yml

@@ -22,6 +22,7 @@ jmri_lcrr_branch: "main"
 
 # SSH key for jmri user (for jmri-gui X11 access — set per-host in host_vars)
 jmri_ssh_authorized_key: ""
+jmri_ssh_authorized_keys_extra: []  # additional keys (e.g. operator laptops)
 
 # SSH key for jmri user → Gitea
 jmri_gitea_key: /home/jmri/.ssh/id_ed25519_gitea