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/host_vars/main-street-station/main.yml

@@ -0,0 +1,16 @@
+---
+# Host-specific vars for main-street-station (JMRI headless server)
+# LCRR - Lake Country Railroad, Milwaukee Road Oct 1956, HO scale
+
+# JMRI profile ID — find with: ls ~/.jmri/profiles/ on the old box
+# Format: <name>.<8-char-hex>  e.g. LCRR.3d3f1dfc
+# TODO: fill in after restoring config from GitHub backup
+jmri_profile_id: ""
+
+# USB serial device for NCE command station
+# Verify after install: ls -la /dev/ttyUSB* /dev/ttyACM*
+jmri_serial_device: /dev/ttyUSB0
+
+# Path to JMRI config backup for restore task (leave empty to skip)
+# Point at a local checkout of the LCRR GitHub repo
+jmri_config_src: ""