feat: add JMRI headless server role and main-street-station host

- New ansible/roles/jmri role: installs OpenJDK 21 headless, creates
  jmri service user, downloads JMRI 5.10, deploys JmriFaceless systemd unit
- Handles dialout group membership for serial device access
- Config restore task for post-reinstall recovery from GitHub backup
- host_vars/main-street-station: profile_id and serial device (TODO: fill in)
- Inventory: jmri_server group with main-street-station at 192.168.10.45
- Playbook: day1_deploy_jmri.yml (linux-baseline + jmri)

ansible/roles/jmri/handlers/main.yml

@@ -0,0 +1,9 @@
+---
+- name: Reload systemd
+  ansible.builtin.systemd:
+    daemon_reload: true
+
+- name: Restart jmri
+  ansible.builtin.systemd:
+    name: jmri
+    state: restarted