jmri: replace TigerVNC with Xpra for JMRI GUI display

VNC had window management issues and some dialogs wouldn't open correctly.
Xpra runs in rootless mode — each JMRI window appears natively on the
client without a VNC client or XQuartz required.

Changes:
- Remove tigervnc-standalone-server, jmri-vnc.service, .vnc/ directory
- Install xpra, deploy jmri-xpra.service.j2 (systemd unit)
- Update jmri-gui wrapper: DISPLAY=:100, attach instructions printed on launch
- Update defaults: drop VNC vars, add jmri_xpra_display=100
- Rename handler: Restart jmri-vnc -> Restart jmri-xpra

Connect from macOS/Linux:
  xpra attach ssh://jmri@main-street-station/100

ansible/roles/jmri/templates/jmri-gui.j2

@@ -1,22 +1,22 @@
 #!/bin/bash
-# jmri-gui — launch JMRI GUI on VNC virtual display
+# jmri-gui — launch JMRI GUI on Xpra virtual display
 # Managed by Ansible — do not edit manually.
 #
 # Usage (connect as jmri user):
-#   ssh jmri@main-street-station jmri-gui panelpro
-#   ssh jmri@main-street-station jmri-gui decoderpro
-#   ssh jmri@main-street-station jmri-gui status
+#   jmri-gui panelpro       Launch PanelPro on Xpra display
+#   jmri-gui decoderpro     Launch DecoderPro on Xpra display
+#   jmri-gui status         Show service status and attach command
 #
-# Then connect a VNC client to main-street-station.local.mk-labs.cloud:5901
-# VNC password is in the Ansible vault (vault_jmri_vnc_password)
+# Then attach from macOS/Linux:
+#   xpra attach ssh://jmri@main-street-station/{{ jmri_xpra_display }}
 
 set -euo pipefail
 
 JMRI_DIR="{{ jmri_install_dir }}"
 JMRI_SERVICE="jmri.service"
 MONITOR_SERVICE="jmri-monitor.service"
-VNC_SERVICE="jmri-vnc.service"
-DISPLAY=":{{ jmri_vnc_display }}"
+XPRA_SERVICE="jmri-xpra.service"
+DISPLAY=":{{ jmri_xpra_display }}"
 export DISPLAY
 
 usage() {
@@ -28,13 +28,13 @@ status() {
     echo "=== JMRI daemon ==="
     systemctl status "$JMRI_SERVICE" --no-pager -l 2>&1 | head -8
     echo ""
-    echo "=== VNC server ==="
-    systemctl status "$VNC_SERVICE" --no-pager -l 2>&1 | head -5
+    echo "=== Xpra display ==="
+    systemctl status "$XPRA_SERVICE" --no-pager -l 2>&1 | head -5
     echo ""
     echo "=== Layout monitor ==="
     systemctl status "$MONITOR_SERVICE" --no-pager -l 2>&1 | head -5
     echo ""
-    echo "Connect VNC client to: $(hostname -f):{{ jmri_vnc_port }}"
+    echo "To attach: xpra attach ssh://jmri@$(hostname -f)/{{ jmri_xpra_display }}"
 }
 
 launch() {
@@ -47,32 +47,31 @@ launch() {
         *)          usage ;;
     esac
 
-    # Ensure VNC server is running
-    if ! systemctl is-active --quiet "$VNC_SERVICE" 2>/dev/null; then
-        echo "Starting VNC server..."
-        sudo systemctl start "$VNC_SERVICE"
+    # Ensure Xpra display is running
+    if ! systemctl is-active --quiet "$XPRA_SERVICE" 2>/dev/null; then
+        echo "Starting Xpra display..."
+        sudo systemctl start "$XPRA_SERVICE"
         sleep 2
     fi
 
-    # Stop the JMRI daemon if running
+    # Stop the JMRI daemon if running (we're taking over the hardware connections)
     if systemctl is-active --quiet "$JMRI_SERVICE" 2>/dev/null; then
         echo "Stopping JMRI daemon..."
         sudo systemctl stop "$JMRI_SERVICE"
     fi
 
-    echo "Launching $binary on VNC display $DISPLAY..."
-    echo "Connect your VNC client to: $(hostname -f):{{ jmri_vnc_port }}"
-    echo "VNC password: see Ansible vault (vault_jmri_vnc_password)"
-    echo ""
-
     # Force AWT out of headless mode
     export JMRI_OPTIONS="-Djava.awt.headless=false"
 
-    # Launch on the VNC display — no --profile so JMRI uses last-session preference
+    echo "Launching $binary on Xpra display $DISPLAY..."
+    echo ""
+    echo "Attach from your workstation:"
+    echo "  xpra attach ssh://jmri@$(hostname -f)/{{ jmri_xpra_display }}"
+    echo ""
+
     "$JMRI_DIR/$binary" &
 
-    echo "$binary launched in background on VNC display."
-    echo "Close it from the VNC client, then run 'jmri-gui status' to check state."
+    echo "$binary launched. Attach with xpra to see windows."
     echo ""
 
     # Restart daemon if layout switch is still on