feat: independent fullscreen kiosk display foundation (#1)

Kiosk process owns its display lifecycle: waits for X11, keeps the
fullscreen black canvas below video, stops deterministically on signal.
Supervisor starts it before video, restarts only on process death, and
shuts the whole process group down; X11 downtime never restarts the
supervisor. Per-target opener/template abstractions for future MIPI.

deploy/config.yml

@@ -1,3 +1,12 @@
+display:
+  enabled: true
+  # Independent kiosk canvas process. It waits for X11 itself, keeps the
+  # fullscreen black canvas below video, and stops only on shutdown.
+  command: /usr/local/bin/groundstation-display
+  user: orangepi
+  display: :0
+  xauthority: /home/orangepi/.Xauthority
+
 serial:
   path: /dev/ttyS0
 

deploy/groundstation.service

@@ -1,5 +1,5 @@
 [Unit]
-Description=Ground Station RC and video supervisor
+Description=Ground Station RC, kiosk display and video supervisor
 Wants=graphical.target
 After=graphical.target display-manager.service