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
62e9f13a45