fix(desktop): remove forced 1920x1080 modeline, limit LightDM restarts

On real server hardware (IPMI/BMC AST chip + nomodeset) the VESA
framebuffer is set by BIOS at whatever resolution it chooses (often
1024x768 or 1280x1024). The hardcoded 1920x1080 Modeline caused X to
fail → LightDM crash-loop → SOL console flooded with systemd messages.

- Remove Monitor section / Modeline from xorg.conf — fbdev now uses
  whatever framebuffer resolution the kernel provides
- Add lightdm.service.d/bee-limits.conf: RestartSec=10,
  max 3 restarts per 60s so headless hardware doesn't spam the console

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

iso/overlay/etc/X11/xorg.conf.d/10-fbdev.conf

@@ -4,19 +4,8 @@ Section "Device"
     Option      "fbdev" "/dev/fb0"
 EndSection
 
-Section "Monitor"
-    Identifier  "monitor0"
-    Modeline    "1920x1080" 148.50 1920 2008 2052 2200 1080 1084 1089 1125 +hsync +vsync
-    Option      "PreferredMode" "1920x1080"
-EndSection
-
 Section "Screen"
     Identifier  "screen0"
     Device      "fbdev"
-    Monitor     "monitor0"
     DefaultDepth 24
-    SubSection "Display"
-        Depth   24
-        Modes   "1920x1080" "1280x1024" "1024x768"
-    EndSubSection
 EndSection