feat(boot): set 1920x1080 resolution for framebuffer and GRUB

- Add video=1920x1080 to kernel cmdline (sets fbdev to Full HD)
- Update GRUB gfxmode to 1920x1080 (fallback to 1280x1024,auto)
- Add Xorg Monitor section with 1920x1080 Modeline and preferred mode

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

iso/builder/config/bootloaders/grub-pc/config.cfg

@@ -8,7 +8,7 @@ else
 fi
 
 if loadfont $font ; then
-    set gfxmode=800x600
+    set gfxmode=1920x1080,1280x1024,auto
     set gfxpayload=keep
     insmod efi_gop
     insmod efi_uga